I know this is an old thread, but I wanted to add information to it in case someone else is looking for details on pooling.
The VRD mentioned in this thread is an excellent resource, and should be reviewed prior to doing the pooling.
With the hash assignment option (the default for pools), a client will retain the IP address and vlan they are initially assigned. This is important where your clients connect to specific services that require, or work better, when they keep the same address.
With the even assignment option, clients may get different IP addresses as they move from AP to AP. This can be made to work like the hash option by setting the "Preserve Client VLAN" option in the VAP.
We had a problem where our Pool was not honoring the hash option, and the fix was to recreate the pool and reassign it to the VAP's.