Whilst I agree in part that 50mm is "neither here or there", there is a use for it.
I am a BIG advocate of the 35mm focal length, especially on prime, way before the Sigma 35mm came along, it has been to Rome, Hong Kong 3 times, Florence, New York, Atlanta, Scotland, Prague, France, Ireland, and about 40+ weddings, It is one of if not my favourite lens. I love it and will continue to be my go to lens. However, to 50mm's credit, there are times when 35mm is too wide and 85mm is too close. When using either of those lenses feels like it is a compromise on composition. That's when I usually get out the 50mm.
I also love the 50mm on the dance floor pairing with a 24/1.4. A 35/85 combo on the dance floor is not wide enough and too long. 24/35/50 is perfect.
Besides, I already have a 35/1.4, 85/1.2…not bought a lens since December 2012….getting an itch for something new to play with