Centering your control surfaces when setting up your RC plane is a crucial step in making sure your plane flies properly and that you don't have to overcompensate with TRIM on your transmitter to account for the off center servos and control surfaces.
Also, it is cumbersome to have to hook up your receiver, bind it to your transmitter, and center your servos by using your radio. It is definitely doable and there isn't anything wrong with doing it that way, however, it is way easier to have a servo test that can center your servos for you without having to use the radio to do this.
The servo testers are very inexpensive and they can also be powered by a 2 cell LiPo battery as most require between 4 and 6 Volts. Be sure not to cross the wires though as I learned this the hard way and wasn't paying as much attention to the pin out as I should have been and I started to see smoke! Fortunately, it didn't fry it, since I caught it in time. The pin outs should give you the negative, positive, and signal designation. So again make sure you have it plugged in the right way.