Why so many tartans per clan name?

[mcclainms72]

I understand why there's modern and ancient versions, and I guess I see why there's dress and hunting, but where do all of the others come from, and do they each have a purpose? Maclean of Duart also has muted, burgundy, weathered, etc.- 7 setts and countless colourways.

Are some only appropriate for certain settings or certain members of the family? Some of them sound like they're only pupose is variety, but
I'd like to know if they ALL are. I'm sure that the rules aren't rigid, but I'd hate to wear one because it looks good and then find out it's only for outdoors, wives, family septs, or something.

Anyone know?