uucp and grades

[Frobnitz The Nth]

i've read (in the SUN document "Administering the UUCP System")
 ...
"All UUCP requests are sorted by grade. A grade is denoted by a single
 letter or number, from 0 to 9, from a to z, and from A to Z, where 0
 is the lowest, and Z the highest. Lower grades cause jobs to be trans-
 mitted earlier during a particular conversation. The default grade is N."

are some grades more efficient then others, or are grades just a measure
of importance-insofar-as-time goes?

(is there a really good source of information on uucp? i've read the
 O'Reilly Nutshell book, and all my ISC 3.2.2 manuals, and the AT&T
 User/System Admin's Ref, but I NEED MORE DATA! MORE! MORE DATA! MORE!!)