I guess the best example I can give is this. 

With Sculptris I can quickly, cleanly and easily make some pretty decent looking stuff that's completely bump mapped, textured and painted.

But if I went with Sculptris and Sculptris only, I wouldn't be learning modeling.

I think the one main thing to consider is that if you find yourself in a situation where your models are going to have to meet specific requirements for games, video or print, you're going to want to know how to model the prehistoric way so that you have complete control over your texture resolutions, poly counts and such.