This is probably a foolish one, but...
So you can force carbonate with a keg (or sugar carbonate, but of course why would you), and then serve from the keg with the CO2 to help dispense.
But, if one wanted to get a couple of kegs but only a single CO2 tank, is that a normal manageable setup?
I would conjecture that the procedure is: ferment (in primary), carbonate in keg (either priming or force), dispense (for keg 1). Then is it acceptable practice to repeat into keg 2 (3, et al) by removing the tank from keg 1 and using it on 2, and 3, and then simply moving the tank back to whichever one you want to dispense from when you are ready?
I.e. does there need to be a constant tank hookup (I would think no, the keg itself is air and pressure tight?), or can you make the most of your investment by cycling through a tank or two to pull off beer from multiple kegs as desired?
Edit: Clarified that I meant ferment in the primary, NOT in the keg!