FS can at times have more detail than its WS counterpart in the 4:3 area, as well as a few other technical uses.
That and I find it enjoyably nostalgic from time to time.
Yeah, you’d always loose horizontal information with full screen, even if they opened up the frame. More vertical information is neat though, until studio lights and boom mics start showing up.
Star Trek VI was a good example of this: http://imgur.com/a/94kBs