I was wondering whether a team would do better in say, the World Series, if they had swept the NLCS and had time to rest, or if that long layoff was a bad thing.
Here are the results of every 5 and 7 game series since 1969, based on how long a given team's series took, how long their opponent's took, and who won:
Here's the same data except collapsed, ignoring opponent's number of games:
I didn't realize how rare seven-game sweeps in the LCS were-it's only happened six times, but only one team has ever swept a best-of-seven LCS and then gone on to win the World Series - the 1995 Braves.
Looking at the data, it looks like sweeping a series is really bad - when a team sweeps a series, it only wins the following series 18 of 47 times, or a .383 winning percentage, or roughly the equivalent of being replaced by the 2013 Marlins.
But going the full 5 or 7 games isn't great either - teams that use all the games to win a series have won just 23 of 49, a .469 winning percentage.
So it looks like both points of view are correct - when you sweep, you get too much time off and you are rusty for the next series, but if your series goes the full length, you'll be too tired/worn out and also perform poorly in the following series. It looks like the best thing to do is to win a best of 5 in 4 games, or to win a best of 7 either 4-1 or 4-2 to have the best shot at winning that next series.