Incline Push-Ups

I'm still not fully knowledgeable on whether or not incline push-ups are useful to work your lower chest. Declines work the upper chest, so logic tells me incline works the lower chest. I haven't assigned any sets to the inclines, but if I fail a set, I'll finish it with incline push-ups. This doesn't happen often, but it's worked in my favor. If you never fail any sets, then I'd suggest doing 30 or so either before or after the majority of push-ups.