I guess it depends on what you need. Most of them are helpers to create quick applications, ideal for startup and prototypes. Writing less code also mean writin

I guess it depends on what you need. Most of them are helpers to create quick applications, ideal for startup and prototypes. Writing less code also mean writing less bugs. When I create a stylesheet, it may take a while to get feedback if it doesn't work on a obscure browser version while a bug in Twitter's bootstrap will be detected (and probably fixed) a lot sooner.