Do you really need to reboot your Linux server after an update?

For anyone who s ever maintained a linux server, you know that updates are easy, but after almost every one, it says: *** System restart required *** I started wondering if rebooting was really required, since sometimes you have mission-critical or otherwise busy servers, and rebooting is going to cause a problem for your users. But-- what if you need to reboot due to a security update or…