Tablebases have, in some cases, drastically altered the understanding of endgame theory; some positions have undergone complete reversal of results. Tablebases have calculated mates in more than five hundred moves which is beyond a human.
It's important to remember that tablebases ignore the fifty-move rule though and as a result in 1974 FIDE changed the rules several times to account for such positions, but then in 1992 they rescinded these exceptions and restored the fifty-move rule. In 2013, ICCF changed the rules for correspondence tournaments starting from 2014 - a player is allowed to claim a result based on a six-piece tablebase and the fifty-move rule is suspended and number of moves to mate is of no significance. Of course, all this information requires a lot of memory…the seven-piece tablebases require more memory than our home computer will ever have.
If you are serious about studying endgames or are a serious correspondence player, the Lomonosov Tablebases might be a worthwhile investment.