I was watching videos and came across this one.

http://www.youtube.com/watch?v=bT8A7Vc-2SI

IT says that if you just do dumbell presses this will cause you to have all the muscle on one area of your shoulder which won't be good because of the symetry causing joint problems or something. It will also look stupid, and I think I'm developing this big "blob of muscle" in the front like he mentioned.

I've been alternating between dumbell presses and barbell presses, will just doing this exercise for shoulder work cause the symetry to be off like he said? I mean I also do benchpress and rows which work your shoulder. Should I also be doing other shoulder work?

My other question is, when doing dumbell presses and barbell presses is it better to be standing? I was sitting on a bench while doing barbell presses recently and I feel a lot of stress in my back, must be the way I was bending it to help push the weight up.