It's not a size issue. It's a convience issue. Okay lets see if I can express this one better.

A 35mm is similar to a writers notebook. Small enough to carry 24/7. Full of ideas. Mostly not very good. Some okay and a few very good. While you could write a whole novel on a pile of bar napkins it's not the best choice-)

It lets you take risks. Try things you might not with a larger camera. The same way a notebook lets you write down a half baked idea. I'm not saying this is the only way it can be used but that it shouldn't be seen as a negative.