This means you can setup an SM to register to multiple APs. If you have customers that can see other APs at a [...]]]> Color Code Priority on SM
On the SM, multiple color codes (up to 10 per SM) and priorities (3) allow more control of which AP an SM will register to during normal and off-normal conditions.

This means you can setup an SM to register to multiple APs. If you have customers that can see other APs at a decent rate it could help if an AP goes down.  The less customers out during an outage the better. Even if they are limping along they could still see another AP.

A good scenario is say you have a Canopy cluster.  You go ahead and throw up an omni.  Have a single AP hooked to that omni.  You have a sector or sectors go out during a thunderstorm.  You could fire up the omni and have your SMs register to that omni while you wait on climbers or the weather to clear.  My suggestion would be to mount the omni at a different level than the sectors if possible.