/usr is the second major section of the filesystem. /usr is shareable,read-only data.That means that /usr should be shareable between various FHS-compliant hosts and must not be writen to.Any information that is host-specific of varies with time is stored elsewhere.
the important is why put them to somewhere not elsewhere,and for instance,what defferent among /sbin,/usr/sbin,/usr/local/sbin ? that's all we must be know.