An access point will only deliver broadcast traffic to an access point that has a user associated on that VLAN. If you have 10 access points, and a single VLAN and a user associated on every access point, it has to deliver it to 10 access points. If you use VLAN pooling and more than one VLAN in a pool, the access point would only have to deliver the traffic to the access points that have users on the VLAN with the broadcast, so statistically it could be less based on the fact that you would not have to deliver a broadcast to all users.
After VLAN pooling was created a number of methods were introduced to control broadcasts like broadcast filter all, airgroup and dynamic multicast optimization that go even further than just statistically to drop broadcasts, so that VLAN pooling is not the most effective thing that can be used to control broadcasts. Running broadcast and multicast applications on wireless and is very inefficient. You could just have "drop broadcast and multicast" enabled at the VAP level and use a single VLAN and not have to deal with any unwanted broadcasts. Airgroup could also manage mdns and dlna traffic so that devices can discover each other without the broadcast overhead. This is far more effective to control broadcasts than VLAN pooling. VLAN pooling is still very good when you want to just add a VLAN capacity to a network without having to change subnet masks on all of your clients.