Why?
1. You can get up close and personal (not that I have in this gallery!) with its 21mm equivalent -even into someone's comfort zone- point the thing somewhere else, and still include a human subject without fear of them being too weirded out;
2.Fine, graded bokeh at f2.8 ...yet massive depth of field and ultimate sharpness with just a wee quick click to f4 or 5.6, with a small "throw" if manually focusing;
3. With such a wide angle of view, you can alter composition dramatically with little apparent movement: a quick flick to an area of average "grey" ....lock AE ...recompose with another flick without drawing attention to oneself, and dink ...job done.

Here used on my XT-1 in Bath, UK.

Shauny, Jan 2017