I use it a lot! The SB tablet is the state of the art (sadly, because evidently there have been no advancements). Nothing is so light: even the Surface Pro X is inferior (13.5"/730g vs. 13"/770g). This comes from the interesting design choice of stripping as much as possible from the tablet itself (the Surface Pro instead, is intended to be more functional, when in tablet form, since it's coupled with lightweight bases).

In the past, I used it primarily to read electronic versions of several paper magazines; this format is (IMHO) best read on a large screen - the sweet spot is around 14, so 13.5 is the closest (I reckon the 15" is too big; the SB laptop form factor has a bulky design).

In the present, I use it for studying (textbooks, mostly) - for textbooks, even 12.x" is fine, so even a Surface Pro would do.

Having said that, I like it as a tablet so much that I've pretty much ditched the base and bought another laptop for development. The SB laptop form factor just sucks (IMHO), as it's very bulky, and Microsoft has an insane pricing strategy, that makes it unjustifiably expensive for developers looking for a serious dev machine. Nowadays it's more competitive due to being old, but the 16 GB models have never been competitive, both in price and form factor, to competitors like the Dell XPS.

Of course, I don't imply that many people use it this way because I do, so I really don't know the general use cases :-)