from the Zone Director online help guide:
The maximum number of WLANs configurable per ZoneDirector controller are as follows:
On single and dual-band 802.11n APs, the maximum number of service WLANs deployable per AP radio is 27. These APs support maximum 32 SSIDs per radio, but five are reserved (two mesh SSIDs and one each for monitor, recovery and scan).
802.11ac APs support up to 27 service WLANs on the 2.4 GHz radio and 13 service WLANs on the 5 GHz radio.
CAUTION! Deploying a large number of WLANs per AP will have a performance impact. Ruckus Wireless recommends deploying no more than eight WLANs per AP radio.
The ability to create numerous SSIDs above a practical limit could be for situations where they are switched on and off by schedule.
not the one I was looking for... but does have a pretty picture.