I recently downloaded TBB41_20130613 (current release for Windows at this time), and I noticed that there are folders for vc11 and vc11_ui bin/lib folders. As far as I can tell, both have the same libraries (file names are the same), but they are clearly different binaries (different file sizes). I haven't found any reference in the documentation or via Google what's the difference between the two.
What's the difference between the two? When should I use one over the other, or must I reference both at the same time?