As someone who winds up doing a lot of dup cleanup and merges -- IME, cleaning up the best profile, and cleaning out the others before the merge is by far the easiest thing to do.
Bios are usually chronological (or most-important-thing followed by chronology,) so working through two of them side-by-side is pretty easy: "Yup, have that; oh, great source, pull that in; hey, that's garbage, toss it."
But once they're all combined in a single bio, the logic and easy side-by-side comparison is lost.