I tweaked a hamstring enough last winter that i was off the bike and in physical therapy for 6-8 weeks. I stretched a lot in PT and continue to stretch 3-4 times a week now, after a ride or after a shower. It's helped my position on the bike quite a bit, in that I am more comfortable now than I was before. I'm also positioned more aggressively now than I was before.

I've seen a benefit without any downside, but as with everything YMMV.