Anything you can do with Pneumatics you can do with motors (and vice versa). Thus it comes down to the application. Most people who use only motors tend to look at each actuator as a separate system rather than as a small part of the whole.
Case in point: If I have a robot that has 7 actuators for a claw / gripper / arm I could use 7 separate motors (each with their own encoders and limit switches
) or I could use 7 cylinders (with hard stops), a compressor and a storage volume (1 system). Each has their place.
Another advantage of using pneumatics is that you can set whether the energy is released or maintained at power-down.
Examples:
1>Say you want a claw / hopper to drop / dump what its carrying at the end of the match ... just set the valve to open the cylinder to atmosphere.
2> say you to ensure the robot does not move (even if on an incline) when power is turned off ... set the valve so that when power is turned off, pressure goes to a cylinder that lifts the robots wheels off the floor.
3> (from a couple of years ago) Launching a tether back to your side of the field to score points in a zone.
Energy wise both use approximately the same amount of energy, but the pneumatic system uses it over a longer period of time (utilizing stored energy much better), thus lowering the chances of 'popping' a circuit breaker.