[Johnny9ball]

I normaly go with one sketch color for the entire model. What I like to do is assign different basic color to surfaces to help me differentiate the model surfaces visualy.

You can use it for whatever might help you. If you wanted to visually seperate the model into parts that you can easly see by color then changeing the sketch color might help a lot. For instance if someone likes to assign surface colors and such when they are done with modeling they might assign different colors to the wires to help them visually seperate the model into parts that they can easly see by color.