From my own experiments I have found if I do sets of push ups throughout the day, in sets I get a more leaner physique. I am a big believer in the "greasing the groove" method. I do alot of push ups with resistance (resistance bands and the power push up) and find my core gets tighter (stability) and worked more.

My big interest in push ups came from an old IronMan magazine I found years ago. It had an article on the old school bodybuilders who did all kinds of push up variations. Another reason was a old mma fight years ago. One of the fighters did these crazy hard punches. Every time he landed it was like a whip. He literally locked out on every punch. If you don't know what I'm talking about just watch people on focus mitts. They do these half punches. I thought if I can do alot of push ups it would help me punch at full extension and hit harder.

In the end I don't think the push ups helped my punching except for learning muscle tension. Still one of the best exercises in the world.