The soggier they are the better, if you're putting them somewhere open on all sides. Up against a building, in a moist climate, if the wind is not very high, you're good to go.
I agree, fallen leaves are wonderful mulch and fabulous soil amendment material. And, they're free for the gathering. But there was one year I spent hours collecting fallen leaves to mulch a new garden that was in a very open area, in an extremely dry climate. I wet them down copiously and thoroughly but they did all blow away all over that flat land beyond. Three times. So, I gave that up, in that spot, with great regret!
