My neighbor uses dried grass clippings, & she always has a beautiful garden.

Their seeds are still alive even when dried.

Most lawn grasses are mowed before they ever get seeds.

I mulch my grass clippings back into the lawn, so I don't use them for mulch.

If you have some grass clippings they make a great addition to your compost pile, but you can use them for mulch too.

IMO, shredded leaves are better for mulch than grass clippings, but its personal preference and a matter of what is readily available.