It takes time but it's well worth it. Browsing through all those grey hairs and only seeing one of each style makes changing my sim's appearences so much less of a chore. Plus no more finding a really nice hairstyle that I want to use but discovering that it's actually purple rather than black and therefore looks ridiculous.
I'm more into pruning. I don't need 3 or 4 types of blonde for a style I'm not that fussed on anyway, and so on and so forth.
I never thought of doing that, although I have to admit I love having as many recolours of each hair as possible (providing they're realistic looking recolours) that way it's more likely that I can match a posh 'up' do with an everyday ponytail on the same sim without having their hair undergo a dramatic colour change when they put on their formal wear.