On March 21, 2019 the provincial elections were held in the twelve provinces of the Netherlands. These elections are also important for the composition of the Dutch parliament as the members of the States-Provincial are the ones electing the members of the Dutch First Chamber later in May. After the official announcement of the results, however, the votes in one of the provinces, Flevoland, had to be counted again at the request of one of the parties, the Christen-Democratisch Appèl (CDA). While the polls on 21 March had indicated that the CDA would receive a total of four seats in the States-Provincial of Flevoland, in the final results the party only received three seats with one of the four predicted seats going to DENK. Because of the small margin of difference in the number of votes for either party, the CDA asked for a recount of the 160,000 votes in Flevoland, which was granted – albeit without any effects on the CDA’s number of seats in the States-Provincial: the allocation of seats remained unchanged after the recount despite small differences in the number of votes for each party.
There are different reasons and grounds, on which a recount of votes in elections can be based.
Firstly, recounts can be mandatory and triggered automatically when the number of votes counted for two competing candidates, or two competing parties, is very close to each other. This can particularly occur in majoritarian systems with first-past-the-post, where a relative majority of votes cast suffices to win. One of the most famous recounts in contemporary history, for example, the recount of the votes in Florida in the 2000 presidential elections, was triggered automatically by Florida State law, which required (and still requires) a recount of votes any time the margin between the winning candidate and the losing candidate is 0.5% or less of votes cast (see Florida Statutes §102.141(7)). While the recount was in the end – not without controversy – stopped by the US Supreme Court in Bush v. Gore, Florida is not the only US State, which has included an automatic recount of elections in its laws. Alabama, Colorado and Washington have similar rules, while laws in Alaska, South Dakota and Texas, for example, only require an automatic recount when there is a tie. Other States such as South Carolina or the District of Columbia in turn have implemented an automatic recount where the margin is 1% or less. 
Secondly, a recount of votes can be ordered due to simple numerical irregularities. This normally happens before the official announcement of election results and is a rather uncontroversial and not uncommon ground for recounts and can occur, for example, where the where the number of votes counted exceeds the number of eligible voters in a constituency. In Germany, for example – where each voter has two votes and can cast a vote for a direct candidate in their district and a separate vote for a party list on the same ballot paper – a recount is always required where the total number of first votes counted, both valid and invalid, do not correspond to the total number of second votes counted. It is for the respective returning officers at district, State and federal level to ensure that no such irregularities are accounted for in the final results (§§76-79 Bundeswahlordnung). Hence, in the 2017 Bundestag elections a recount of votes was necessary in 33 out of 299 districts to clear up numerical inconsistencies. 
Thirdly, it is possible that votes are recounted because an appeal has been lodged against the results of the elections by either voter(s) or losing candidate(s)/political parties. Thus, in a majority of States in the US it is possible for a losing candidate, a voter (or a group of voters) or other concerned parties to request a recount of votes. Similarly, in Germany all eligible voters, the returning officers at federal and State levels and the President of the German Bundestag (but not political parties!) have the right to lodge an objection to an election. However, unlike in the US, no clear rules on how and when a recount of votes is to be granted exist; in fact, German electoral law does not explicitly foresee any such possibility after the official results of an election has been announced. Instead, much discretion seems to have been left to the returning officers and electoral commissions, even if the final responsibility for the scrutiny of elections lies, upon appeal, with parliament and in Bundestag elections with the Bundestag itself (art. 41 Basic Law). Reasons which in the past have led to a recount was, amongst others, a significant divergence in the number of votes counted for a political party in different elections, even though they were held at the same time. For example, in September 2009 a recount of the votes in a district in Schleswig-Holstein was ordered upon request of the party Die Linken after strinkingly less second votes were counted in their favour in the State elections than in the federal elections, even though voters cast their votes for both elections at the same time. But even where there are no signs of irregularities, it is possible that an electoral commission orders a recount in order to confirm close results, as has happened in one district in the 2018 Bavarian State elections, or in the provincial elections in Flevoland in 2019.
But not always are the recounts of votes in an election a warmly welcomed occurrence. On the one hand, voters must be able to rely on an accurate and unmanipulated counting of votes in a democracy that deserves the name. On the other hand, more often than not the likelihood that recount would actually lead to a change in outcome is very small. Thus, the Bundestag has rejected a request for a recount in the 2018 Bundestag elections on the grounds that a recount would not have any foreseeable impact on the composition of parliament because the margin between the candidates in question was so big that no other outcome of the elections would have been possible even if some counting errors had occurred. The slim chances of a different election outcome must furthermore also be contrasted with the costs that a recount inevitably always entails. In Flevoland, for example, 650 people were involved in the recount of the votes, and a recount of the senatorial elections in Minnesota in 2008 has been estimated to cost almost half a million US dollars.
tHowever, an arguably more problematic issue than the high costs of a recount that does not lead to a different election outcome, would be a recount that does lead to a change of office or change of composition of parliament where such a recount is ordered after a significant period of time has passed. This might happen, for example, where the dispute on whether or not to allow a recount takes so long that by the time a decision is reached on the recount, parliament (or any other elected official) has already been constituted for a period of time and adopted a number of decisions. A change in its composition, which in the most extreme case can even entail a change in majorities, could lead to any decisions taken by parliament thus far being called into question. As a consequence, this means that recounts should always take place sufficiently close in timing after elections, ideally even before the announcement of official results, in order to avoid a situation in which the accuracy of elections could be played against the legitimacy of decisions already taken.
 See for an overview: http://www.ncsl.org/research/elections-and-campaigns/automatic-recount-thresholds.aspx.