Yep. A better question might be "why not just carry a tripod too and be done with it?"

That's really what determines where I shoot 4x5 or 35mm/medium format. If I'm out looking for photos, of relatively still subjects, as my primary activity I'll probably take the 4x5 plus tripod, or possibly the 645 Pro with or without tripod. If I'm doing something else but think I might find something nice to photograph I'll take 35mm or the Yashicamat.