Product and Software: This article applies to all Aruba controllers and ArubaOS versions.
When the stm fast-roaming feature is active, the client can keep several association states with several APs, potentially making reassociation faster.
On the Aruba switch itself, when the user roams back, less CPU is consumed to make the association happen, since the user is already created.
When Fast Roaming is disabled, when the client is going to roam, the AP where the client was previously associated sends a deauth packet to the client.