Originally posted by SumatranRatMonkey:

Also, this means you can (optionally) kill each boss multiple times in the same world! Which there are uses for, as well.

Well, you can kill each boss as many times as you have the summon items for regardless of number of locations. It's more along the reason you first stated, I would gather; to be able to get a reasonably "close" boss location.

Most seeds I try seem to have less locations for Moder than any other boss (typically two). :(