Where with older equipment you might Y servos together, it now is all programed from the transmitter. Many of the big aerobatic planes might have 3 servos on each aileron for a total of 6. From the transmitter each servo can be plugged into the receiver and brought together as one function in the transmitter. Some of it is programming too. There are ways to overlap functions that is above my head when programming. Complex airplanes like jets will have brakes, speed brakes, start, smoke, and other fancy things along with the flight controls, throttle, retracts, flaps. Lots going on. A big TF P-51 would probably have a servo for each aileron and each flap, each elevator, one for rudder, one throttle, retracts, maybe ignition cut off; thats 10. You can still Y things, but most would be programing from the TX. Programing allows each servo adjustment from the transmitter; some of which is more than just simple mechanical servo movement. You can still do it the old way; what counts is getting out to the field and flying.