I have both lenses. The 24-70 is certainly sharper, but the 50 is 2 stops faster (and much lighter). I use the 50 for dimly lit indoor portraits and in cases I want only want to carry a light setup (in which case I may just as well take the 40 pancake). Opinions about the 50 are quite mixed if you browse the internet, but I do like the look. The lens is quite soft, so I typically stop it down to 1.8 or 2.0.
I have both lenses and plan to keep both. I also use the 50 1.4 for indoor portraits and shots of the kids. Its certainly not as sharp as the 24-70, but you don't need razor sharpness for portraits. I can achieve better subject isolation with the 50 and the bokeh is very nice.