We have certain days for pickup (3 times a year I believe). They don't take large amounts, they will only take things that are in brown paper bags, or that are tied and no more than 3' in length. I always haul the clippings away.
Where I live we have to pay to dump grass clippings, but we are allowed to dump brush for free. I put any grass clippings I have in the bottom, and cover it with hedge clippings. Then I get to dump everything for free- as long as they don't catch me haha