Hrm. Skim ahead if you already know some of this… So say you have a running program XYZ that loads libUseful.so to do useful things. Now you run some updates and libUseful.so gets replaced with the new version. Because of how files on Unix work, the old version still exists on the disk until XYZ closes it, but any new program will load the new version. So things generally “just work” when the system is updated in place, but on the rare occasion causes weird problems. Fedora (from the GUI) chooses to run updates during reboot to prevent the rare, weird problems. If you update from the command line, it just does them in place. Kernel updates always require a reboot to apply though.
Hrm. Skim ahead if you already know some of this… So say you have a running program XYZ that loads libUseful.so to do useful things. Now you run some updates and libUseful.so gets replaced with the new version. Because of how files on Unix work, the old version still exists on the disk until XYZ closes it, but any new program will load the new version. So things generally “just work” when the system is updated in place, but on the rare occasion causes weird problems. Fedora (from the GUI) chooses to run updates during reboot to prevent the rare, weird problems. If you update from the command line, it just does them in place. Kernel updates always require a reboot to apply though.