As you get a bit more advanced, your prob going to want to do vlans on your wireless networks and even wired networks, etc. In that case get a vlan capable switch and your AP.. you would then be able to leverage any interfaces in pfsense as other networks either via physical or vlans, etc.
Network interfaces make really poor switch ports.. If your at a point where your thinking - oh I can bridge one of my interfaces on my router to use as a switch port.. Your going at the problem the wrong way - clearly you need another switch or higher density switch at that point ;)
Like saying hey I need to drive this nail in to that piece of wood.. Oh shit my hammer is on the other side of the room - let me just use this screwdriver I have to hammer it in.. Its got a big handle on it ;) I will just hold it by the shaft and swing it like a hammer. While it might get the job done - its not the proper tool for the job.. Its not really designed to do that.. Your prob going to miss the nail and slice up your hand, etc. etc..