It's more beneficial to have bigs that are capable of playing both spots.... meaning size is paramount. AB can play both, Amir is showing to be capable of at least playing meaningful minutes at both, Ed seems a bit small to play C but maybe he's just not physically developed enough. Even last year AB was guarding C's and PF's, but his point was that he didn't want to guard much bigger, stronger players all the time.... and why would you want your most skilled players getting beat up anyways. It's the same argument that Bosh
made, as Horford has made, as Brook Lopez has made. It's elementary baby!