Poe switch gives you the freedom of installing wireless access points anywhere a ethernet cable will go. Before power over Ethernet was available a wireless access point always had to be near a power outlet to give it power. This meant more money and usually bad placement.
PoE uses a device called a power injector to transfer the correct amount of power required to run the wireless access point. PoE uses the two unused wireless in a Ethernet cable to run the power. Gigabit Ethernet voip phone manufacturer uses all the wires in an Ethernet cable thus PoE is not available for Gigabit Ethernet. Each client device that meets the standards of the PoE 802.3af amendment will be assigned a power class of 0-3 which will mandate how many watts they need. Often your wireless access point will be managed by a switch that will double as a PoE injector.
Wireless access point placement is a major key for good security, both physical and wireless. If you are using a Fat access point which is located near a common power outlet or easily in reach of employees all it takes is a paper clip to reset the access point and your network has been hacked. Also placement is a major concern because if you install a wireless access point on the perimeter walls of you office you have just sent half you signal out side to the war driver passing by.
Remember when coming up with your wireless network budget do not let anyone say we don't need 12 port poe switch. Compromising on placement of your access points will cost you security and money in the long run.