All the holes on the servo arms are for the adjustability of your control throws. The further the hole from the center of the arm, the more control surface deflection you will have. Also, the further from the center, the less torque you have. The difference is not noticable in most applications. I usually keep mine at about 2-3 holes out on the servo, and then adjust the throw on the control horn on the elevator. All the options are for adjustability, so you can get the throws you want without needing a computer radio.

Silent J