I have worked for a university and several organizations that have had basic guidelines like this. It's much more important in large organizations when many small departments or individuals are creating branded things.

One sees this basic type of thing in press kits and even (er, kinda) "link to us" or "powered by" graphical widgets, but the focus on consistent color and typography are things I think could stand to get some more attention. This type of reference is especially helpful for non-designers who aren't immediately inclined to think about consistency and branding.