Golf Digest had a pretty good write-up with Bethpage's director of agronomy:
https://www.golfdigest.com/story/a-pga-championship-in-the-northeast-in-may-we-took-bethpage-black-for-a-test-runGenerally, the greens are their best during the early spring (FWIW, I had the distinction of playing the first public round this year!) bc of the poa issue I assume.
However, I strongly disagree that the rough might be somehow easier to deal with in August vs. May. The stuff during the recent NY State Open was nearly impossible - 3 feet off the fairway and you might not find your ball. Somehow, that didn't stop an amateur from shooting 64. Maybe it's maintenance practices, but the rough is always manageable in May. If you don't have narly rough, I don't see any purpose to the narrowness of those fairways. All it does is prevent your shot from ending up in the real crap.
They actually thinned the fescue before the Barclays last year, I assume in part to allow for spectator access. I don't anticipate the fescue being as big of an issue, with the exceptions being in the areas around fairway bunkers on holes like 4, 6, 7, 10-11, and 18.