how important is it to keep faces to 4 vertices for rendering? i was watching a video by blender guru and i saw that he was trying fairly hard on keeping all the faces on the mesh he was working on to 4 vertices. think he mentioned that its so that each edge will have a direction or something similar. other than that will it really affect the image quality or show any artefacts in the final render?
It makes a number of things easier and some modifiers only work on quads. One such modifier is subsurf. Also when you need to make a loop cut, it only works on quads. When you hit a triangle or ngon the cut you are making will break there.