It's much easier and cleaner to subdivide quads to refine shapes when modeling. For example, you can split the quads along an entire edge to get a new clean edge for manipulation (ex. to bevel it). If you try to do the same with triangles, you get a jagged mess.
This might be a naive/stupid question, but wouldn't it be relatively easy to merge triangles in the same plane into polygons automatically? (I suppose few triangles from this process would be in the same plane maybe?)
