I know a lot of people advise it, but I prefer grass clippings to be left on the lawn where they break down and feed the soil. But, that's living in a dreamland...cuz rainfall, warm spring rainfall makes grass grow...and grow and when we finally get around to cutting, there's more grass and clippings than we want to be left there.
So we bag...or rake.
Me, I put it all into my compost pile. There is absolutely nothing better to build heat in a compost pile than grass clippings...especially after they have been sprinkled with water. Spread it out over the pile's surface and let it do its stuff.
Then use it around the trees and shrubs.

If perchance, there is more clippings than can safely be put into the pile, then bag it. Throw a little extra stuff in with it, poke holes in the bottom to let the worms in, and put it behind a shrub or hedge and within a short time, it will be ready to take its place in the compost pile.
In the fall, leaves done this way, chopped up with the clippings, are a great way to build leaf mold.

Oh, and throwing a handful or two lawn fertilizer in with the clippings can speed up breakdown.

No! Grass clippings make terrible mulch. They create heat buildup which defeats the purpose of mulching to begin with. They can also change the soil pH over time. It's tied with lava rocks as the worst mulch of all time.

Without seed (weed or grass), and free of herbicides and pesitcides and spread less than an inch thick it would be o.k. and even good but otherwise you are making more trouble.