My cat is a nibbler. She prefers to eat just a few pieces of kibble many times a day. So I leave dry food out for her all the time. And I put her out some canned food at night--not much, usually about an ounce. Sometimes when I get up in the morning she's just nibbled at it and sometimes it's all gone. Some cats will eat everything in sight when free fed, so you can't always do that. But mine stays lean.
Ditto Dr. Doug about fatty liver. Cats are NOT dogs (not that I advocate taking the "they'll eat when they're hungry" approach with most dogs, either).