I don't have any grass, but do use my bread knife for lots of other things around the garden. It's great for trimming the jasmine groundcover along my walkways. As X says, it makes nice straight clean cuts. Also good for digging small transplant holes if my trowel is not handy. Works for pruning and weeding in a pinch, too.
Any serrated knife will do - pruning saw, drywall saw, or I scored a set of cheap steak knives ($4 for a set of 6) like what they have at steak houses, that are very sturdy and serrated. They work great, and I leave them strategically situated around the garden so there's always one at hand.