Does this lens do a good job for photos other than close-up macro shots? For example, does it make sense to use this lens for outdoor family portrait photography? What are some other common uses for this lens?
No. The MP-E is a dedicated macro-only lens. The farthest away it can focus is just far enough to get a 1:1 macro shot. It can only take shots between life-size and five times life-size. The only way you'd be able to take a picture from further away is to adapt the lens to a mirrorless body, and it's not a sure thing that you'd be ablt to focus at infinity even at that.