re: Why put someone back to return punts at all?

You should have the person on your team with the best hands field punts. Catching the ball and keeping it from hitting and bouncing another 10-15 yards is the primary concern. If you get a decent return, that is just gravy. Now if you have a great elusive return man who has great hands then by all means put him back there but the primary concern should be someone who can field the punt cleanly.