Other than booting up into a new kernel, I can't think of any linux
software install process that involves a reboot - and if you're using
ksplice, even booting into a new kernel isn't necessary, as it actually
replaces the running kernel with a new one in-place.

At my day job at a large firm, I manage a number of busy linux
infrastructure servers which have been up for over 1500 days since the
last boot (which was for a kernel upgrade) But I've upgraded
applications and libraries numerous times during the past 3 years - and
nary a reboot required.

As far as building and loading a kernel module, I've never rebooted a
system for that, since the kernel itself isn't changing, you're just
building and loading a dynamic kernel module against the current running
kernel.

In most cases, people reboot linux because either they come from a
microsoft background and think that is how things should be done, or
they don't want to figure out how to load a module or run an init
script, so they just reboot to make it happen.

Other than booting into a new kernel, do you have any specific examples
where a reboot is required?