You Shouldn't Have to Reboot
Only in the most extreme cases
A buddy of mine had a weird problem that sounded like it might have been xorg, or the compositor, or something along those lines. We never got to the point of tracking it down because he rebooted and seems to have solved the problem.
The good bad and ugly of high up time operating systems like linux is that; things can and do break, they can be very difficult to debug, and sometimes the fix is really easy.
I never reboot unless I have to. For instance the laptop I am using right now has an uptime of 123 days. That is only because I left it unplugged and the battery exhausted.
123 days isn't all that impressive for an arch based system (or any other distro for that matter), but the point is…you don't always or even ever have to reboot.
You can just restart an offending server.
Restart your display manager from the command line
From Ask Ubuntu, you will see that all you really need is to determine your default display manager with the following command:
cat /etc/X11/default-display-manager
In my case the result is:
/usr/sbin/lightdm
Once you know the display manager you simply restart it. Now, I only use systemd so I won't talk about the others because I am not interested, but google will answer that question for you.
For systemd all you do is:
sudo systemctl restart <display-manager>
Replace <display-manager> with the result of the earlier cat and in my case you get:
sudo systemctl restart lightdm
That might have fixed the problem which I think resulted from an update.
You don't need to reboot. This ain't windoze.