I guess having both might be something that some people like, but it's not something I tend to lean towards. Especially because you're often better off skewing towards a more even split of colours so that you have colour X available as early as possible.
I don't know how well it would work with things like dual fetches though? Strictly they don't make mana, but if I'm running 8 fetches + 2 duals then I have 10 of that source. I don't expect that there's an easy way of automatically calculating that though, so skipping over that is fair enough.