Advantages of pneumatics
Clean Air is used by a machine & is then exhausted to the atmosphere - no return line necessary.
Any leaks will be of air (which is much less of a problem than oil leaks in Hydraulics).
Availability
Air is freely available in the pneumatics
Most factories are pre-plumbed for compressed air distribution - which makes it very easy to set up a manufacturing process
Simplicity of Design And Control
Machines are easily designed using standard cylinders & other components. Control is as easy as its simple ON - OFF type control
Reliability
Pneumatic systems tend to have long operating lives and require very little maintenance.
Because air is compressable, the equipment is less likely to be damaged by shock. The air in pneumatics absorbs excessive force, whereas the fluid of hydraulics directly transfers force.
Storage
Compressed Air can be stored, allowing the use of machines when electrical power is lost.
Safety
Very small fire hazard (compared to Hydraulic Oil)
Machines can be designed to be overload safe.