BEC are usually more associated with the Electronic Speed Control(ESC).

The problem with more than two servos, or high torque servos, is that they tend to draw more current than a BEC is designed to provide. This will cause the servos to jitter and possibly the loss of control of the model.
If your ESC has a BEC, leave the switch in the off position, and connect a 4.8-6.0 volt battery pack directly to the reciever or via it's own switch.

Some people choose to cut the BEC switch off the ESC so that there is no chance of accidentally turning it on.
I often cut the BEC wires, and solder a two pin deans plug onto the ends. Just in case I find a situation where I will want to, or can, use the BEC in another model.