They can be very helpful, especially when you are a little afraid to use colours together (like purple and green) or when you want to know what colours go with a mexican, indian, gypsy, steampunk... .... theme. Or even if you want to know the colour codes for the Snow White or Evil Queen dress.
By the way I just discovered the Colour Palette Generator. Have you ever seen a picture of a kitchen, bathroom etc. and wanted to create something with similar colours for your sims? Well just copy the url of the picture and paste it where it says "url of image"- it is easy, fun and fast :)
Also Kuler has something similar as the Colour Palette Generator but it is a little tricky to find it so here the direct link to get the colours from a picture (either one from your pc or on flickr). You can also drag the white circles on the picture if you want a specific colour.
Color Scheme Designer
Colour Palette Generator