Preference for tags over categories?

I'm looking at aggregating post information (for menus and the like) across multiple sites for home page and site-wide menus. I've thought of using both categories and/or tags, but I noticed that WPMUDEV seems to provide a bunch of cross-site tag plugins, but none for categories.

Is this the result of a preference for tags in this sort of thing over categories? If so, what's the rationale? (I'm not trying to bust your chops, but really understand if one approach is better/more versatile/etc than another).

Thanks
--David