Your description of how the Enable IP Management option works explains almost everything.  One thing that is different with Enable IP Management turned on is that if there is currently no valid IP address, Fusion will tell Microsoft to attempt to renew the IP address every 10 seconds (Microsoft will also be performing some attempts internally, so there will be a DHCP attempt approximately at 0, 2, 4, 8, 10, 12, 14, 18, etc. seconds into a connection with an AP), while disabling IP management, once Microsoft gives up on trying to get an address, it will not try again (i.e. it would try for some number of attempts at an exponential backoff, but will eventaully give up and that device will NOT get an IP address until the next connection). Note, this only happens when there is no address.  Fusion's management of the IP address is more aggressive, since you really have no point of connecting to the Wireless network if you cannot get an address.  If the customer would rather have less traffic, but time out getting an address, they can select to allow Microsoft to handle it.