It depends what you mean by computer resources. (I haven’t had time to try anything of this sort yet, so this is just speculation…)
If you’re talking about the RAM usage, I’m not sure there’s much that could be done, and even if you could, returning the server to a useable state would still take a few seconds.
If you’re talking about CPU usage, I’m pretty sure that the best solution would be to code a “no players” state in your gameplay code that disables all sources of CPU usage like AI, navigation, etc… You could also lower the framerate drastically, it would be less effective that going deep into your code to disable things, but the ratio effort vs reward would be very high.