Only if you need it. I'm running 5 from a laptop, decent specs (not the best of the best) I have the 4 alts on 1024x768 and the main on 1280x1024. All the graphics are turned to the lowest settings (I've been everywhere before, I don't need to see it rendered in the highest quality again) and of course, all windowed.

I might throw an external monitor on it and move the alts to there, but it'll still all be on the same graphics processor.