One problem that has arisen lately is trying to change (increase) the size of /usr using LVM and resizing the fs.

Recent version of bash now link into the glibc locale funstions. These in turn have links back into /usr/lib/locale. This means that even when pulling the system down to single user, as root you cannot umount /usr. And therefore you cannot resize it without rebooting into a rescue system.

Unix type systems have had the advantage of not requiring numerous reboots for system admin - but this seems to be changing.