Single light photo studio setup vs multiple light setup?

I use a single light setup for photography, its a 1000w light diffused with a white umbrella, sometimes a reflector is used to give the impression of a secondary light source or to deal with shadows and exposure issues. This has thus far provided some good results but i was wondering what studio setup has worked for you and in what situations more is better. Does a multi light setup provide a huge difference in images that can’t be replicated with photoshop?