Each display is different. Display space and cost usually influence personal preference too. Once combined, looking at an individual figure can be a pain (esp. a leg + the combined forms are always at the back of any shelf).

I would rather track down the hard to get stuff and expensive items on my wants list before looking for doubles. And if someone comes over and wants to see Bruticus i think it is more fun to build him right there then to squeeze him out from the back of a shelf.