Do grass clippings left on a lawn contribute to thatch build-up? Is this thatch harmful to a lawn?

With the summer weather comes some inevitable lawn and garden work. For many homeowners, this means cutting the grass. As I watch my neighbors participate in this summer ritual, I’ve noticed there is little consensus around grass clippings. Do you leave them on the lawn, or do you collect them for your compost pile? Do grass clippings contribute to thatch build up? Does this thatch attract harmful insects?

What do you do with your lawn? Please help us answer this hot summer question!