The shoulder press and developing front delts for improvements in chest size could work for some people, and not for others. Its entirely up to your body.
For example, a person with naturally weak front deltoids is going to be held back on the bench because they will give hardly any assistance. Whereas, someone like me, who has WAY overpowering front delts doesnt get any help from it because I have a hard enough time as it is trying to convince my front delts not to do the work. lol
Its gotten so bad for me, mys houlders hurt. My front delts sit probably 1.5" above my biceps when I flex, and they're way out of proportion with my rears and medials, so, during the day, they're constantly pulling forward and causing pain in the joint. I'm trying hard to fix this.
O/T, but on bench, my chest and front delts are very powerful and perform the lion's share of the work, and then I've got these weak ass triceps. EVERY time my tri's give WAY before my chest is worn out.
So, right now, I'm in this fucked up state where a few of my muscles are out of balance and proportion, and its really annoying to me...lol...sorry for the o/t rant.