Splitting hairs

There’s a beauty school nearby, where they train people to become “aestheticians” (but not aesthetologists or aesthetonomists, apparently). Inside, they run a salon where students get to practise on real heads. Out front, their sign lists the prices of various cuts, but has this footnote: “*Long hair may vary”.

What exactly does that mean? After a cut, is long hair hacked and slashed so badly, that it varies from one side to the other? Or does it mean that long hair becomes shorter after a cut? I assumed that would be taken for granted.

I’m confused.