Unity Builds

Is there any point to keeping more than one build at a time?

And if so, what are the naming conventions for builds?

yes.
case 1: networking aka online game. if you want to test a specific feature that should be visible and invisible for the other.
case 2: saving data. you need 2 builds if you want to test with 2 clients with different saves. if you dont you may get an System.IO exception.
case 3: you just want to see your progress in developing.

naming conventions:
In my case I do: PLATFORM_BUILDID
so there is a folder with my gamename. in it a folder “builds” with platformfolders in it.
example: Gamename/WIN_1.0.5

  1. number for major gamechanging update
  2. num for minor update
  3. num for bugfixes etc