Pneumatics are very hard to use when you want precision of movement.
This is because air is compressible: it's like trying to position
something accurately, when you have to push it through a large
spring.

But if you want precision force, rather than precision positioning,
then a natural spring of the right force constant is a good thing.

Imagine trying to pick up an egg with a robotic hand when you have
hydraulic positioning - very accurate but no automatic control of
applied force. Then imagine it when you've got low-precision
positioning but good control over the force applied.

What you really need for a robotic hand is the "right" mix of position
accuracy with adjustable force. You won't always be picking up eggs!

Tim.