How frequently should I patch and reboot?

Hello,

I know it's kind of a dumb question, but any guidelines on how often I should reboot the servers/let the servers run after doing updates? Any risk in updating all the PVE software for a couple months and then rebooting the server only a couple times a year? I have the servers in clusters so down time is not a big issue just wondering how to keep them healthy :).

Thanks

--Will