If you can return grass clippings to your yard that will benefit your grass the most. They can be used as mulch but cut grass will dehydrate much more quickly than real wood based mulch.

Yes, the grass will break down fast, but in the summer when you mow every week, we seem to have lots. We have been using it in the veggie garden as mulch for 12 years now and the soil is black and we have worms. I think it worked.

If you do use it, just becareful not to pile too much too close to the plants as it will get very hot and can kill the plants.

Like Katkin, I use grass clippings as mulch in the veggie garden and it does break down fast! And it gets VERY hot so be careful where you put it.
~Betsy

If you really want to get creative, you can make your own manure using grass clippings. I tried this before we got a mulching blade for the lawnmower and it smelled like the real thing! But, the plants really loved it.

Regina

Here is a link that might be useful: Home made manure

Grass clippings work awesome in wild flower beds .