Though it may not answer all your questions, take a look at the
hier(7) man page...

In message <1.5.4.32.19970522213428.008cd168@mindspring.com>, "Kevin P. Neal" w
rites:
>Why is user email stored in /var/mail instead of /var/spool/mail?
>
>What is the purpose of /var/spool? When machines are news servers, where
>does the news go /var/spool/news?
>
>It seems like spool is meant to be considerably larger than /var, so why
>is mail stored by default on /var/? 
>
>Anybody feel like explaining exactly what "spool" means, anyway? 
>
>Just wondering. 
>
>And while I'm here: Why do so many Unix installations that will never ever
>use UUCP still come default with uucppublic drwxrwxrwx? Isn't that just
>asking for abuse?
>--
>XCOMM Kevin P. Neal, Junior, Comp. Sci.     -   House of Retrocomputing
>XCOMM  mailto:kpneal@pobox.com              -   http://www.pobox.com/~kpn/
>XCOMM  kpneal@eos.ncsu.edu              Spoken by Keir Finlow-Bates:
>XCOMM "Good grief, I've just noticed I've typed in a rant. Sorry chaps!"