I have a tendency to add all the branches, and I seem to find a lot more information on the ones who aren't actually related to me which can be a tad frustrating. (I'm convinced my grandfather's family was either in the witness protection program or were beamed here from another planet.)

I do find that adding in the aunts and uncles, etc., has often helped me to find information on the actual people that I am researching, though, so I'll keep doing it. I currently have over 2200 people in my private family tree, all with sources cited.