The meaning of the term functionality is that an object of any kind is well suited to properly function and work for the purpose the object was created for.

eye contacts?

yes, if you get the right prescription. they are the same as glasses. suited to your eyes.

and you would only need them if you could see properly in the first place.

suited = mat'ím (מתאים)

Carbide dies find use in caliber rifles. Their main use is to make sure that the chamber can properly fire out shots. They are more suited for straight well cases.