I hear ya re: form. I think I do a decent job with my bench press form (puffing out my chest throughout the movement) but I seem to always feel "atleast some" fatigue in my front delt. I thought everyone did?
Anyway I was more thinking that I love to do the over head barbell press on shoulder day. I am pretty sure that movement uses quite a bit of tri's. So I was thinking that might not workout too well if you too well if you tore up tri's the day before.

To me the bottom line is if your getting bigger and stronger then your doing something right. When your progress slows, its time for a change up. And remember If your working out like a madman, rest is your friend.