You can keep a team from imploding, but HCs can't artificially create the intensity and motivation that comes from a PO run. In fact, try too hard and your players will just tune you out.
I mean most players aren't stupid, they know the games don't matter, that they're just playing for the stats and pride.
But a lot of players have regressed b/c they were rushed to the NHL before they were ready.
However, no one has been able to point out to me a player who's career was ruined by spending an extra season in the AHL.