It allows you to keep your arms shoulder-width apart which makes it easier to avoid hunching.

It allows two people to have better posture when they're both hacking into the mainframe on the same keyboard.

Even just a keyboard with left and right halves angled toward the respective arms would help. Because with a typical keyboard, the arms come at it at an angle, and then the wrists are crooked to have the fingers on the straight key rows. An angled or split keyboard allows to keep the wrists straight.