After 15 years of lifting and doing my chest and shoulders on different days, I started doing chest and shoulders on the same day about a year ago. It has been one of the best changes i've made to my workouts.
My chest and shoulders has always been my strength. But lately I have been really concentrating on only doing one chest "press" related exercise (incline presses) to focus on developing the Pec Minor groups. See Franco Columbo's upper pecs and his separation - probably the best chest ever imo. That is key to those side poses and flaring those pecs way out. Anyway, both shoulders and chest press movements utilize similar secondary muscles so much, it is really silly to not work them together unless your shoulder workouts are solely isolateral lifts (like rear and side raises) and no press movements at all - which usually is not the case. Plus once you've trained presses for chest, these secondary muscles are so exhausted, you really key in on delts solely when pressing after chest. Talk about burn and pump .. wow.
Also, I cycle my chest/shoulder workout. Week 1 starts chest. Week 2 starts shoulder.
Combining the 2 muscle groups and the added rest of only training these and the secondaries once a week, I am pushing more weight than I ever have.
GL. Bula