Night bus coverage out to the limits of the tube is pretty good (e.g. I used to live on the Harringay ladder and the N29 runs direct from central London; honestly I'm not sure the night tube would make getting there at night any quicker, since it's right where St Ann's Road (Green Lanes) station on the Picadilly line isn't. The night bus to where I currently live goes all the way out to Enfield.
It's often not too bad if you're leaving from Soho, but redevelopment has pushed lots of entertainment out of Soho, so I'm likely to be starting my journey home from Camden, Islington, Shoreditch or Waterloo.
If the tube ran at night, I could reasonably stay out late in Zone 4+! I can't remember the last time I did that. (Why might I want to? Because people live there, and have BBQs etc.)
