The friction discs just like the clutch pressure plates wear and distort with years of constant use (abuse?).
So, if the machine has a clutch that is stiff to operate, has a 'wooden' feel, or worse has started slipping and generally spoils your riding pleasure, perhaps an overhaul will sort out the problem?
Replacing as many of the worn or wear-prone parts as possible will give you a better chance of a perfect, easy to operate and modulate clutch assembly.
More related components below: