"In real(!) life" ...
... there's
more than one(!) potentially-compelling reason to "reboot the system," and the
second one is:
. . . to be 100% certain that the
post-boot initialization sequence, whenever completely completed (from scratch),
d-o-e-s result in a completely-stable system configuration.
"Yessirree, every daemon, upon completing its own particular initialization sequence at its own appointed time and according to its own appointed initialization schedule, d-i-d come up cleanly."
Although "strictly speaking, a 'reboot' is only required when the
kernel-level environment has changed," the
overall startup sequence is a very-vulnerable (and uncertain) time that must be carefully checked "before you get on that plane or take your sweetheart out to a movie."
(Nothing spoils 'a romantic moment' more swiftly than a pager!) 
