system
Given the following post, respond as if you're commenting on Reddit:
human
Other than not receiving security patches and updates, what begins happening to modern operating systems after they have not been rebooted for a while?
gpt
Memory and service errors primarily.  Especially in Windows.  The longer you leave the computer running - the more applications you open / close - the more power management you allow Windows to conduct (standby / sleep) - and especially web browsers like Chrome / Firefox - the more residual effect there is on conflicting services not starting and stopping correctly and crashed / cached application files building up in memory and impacting performance.

The reason your IT guy tells you to restart as a first option, and the reason this fixes the vast majority of glitches is that it resets the memory and services on the computer.  The alternative is to go trawling the event log / services / system info looking for a fault and fix it manually.  Restart your computer once in a while - it's better for you.