"It's a question we all face when mowing: Should I bag my clippings or leave them on the lawn? In most cases, the answer is easy: Leave the clippings on the lawn! Leaving the clippings will save you time and energy, and it will return valuable nutrients to the lawn."
If you have leftover clippings, another good option is to mulch your garden with same. Says Scotts:
"Grass clippings can also be collected for use in a compost pile or as mulch, unless you recently applied a weed control product to the lawn."