645's are (were) for wedding photographers. That's all the redeeming quality I can see in one. You can't buy 220 any more, so it can't replace a 35 for shooting willy-nilly. And it can't do what a 67 can do in terms of neg quality. It's closer to a 35 than anything else, so why not stick with a 35? Just extra bulk and expense for diminishing returns. Unless you're a wedding photographer still using one. Then you're a poor man because the digital people are killing you.