This was hashed out a few months ago so the CONCH-L archives
has plenty.
If I recall the outcome, "cf." is for the Latin "confer" as the
correct sense was something like "as opposed to" or "is clearly
different from" but it seems to often be used in a sense of
"seems to be similar to."
Check the CONCH-L archives and you'll find plenty.
Aloha,
Bob Dayle (a.k.a. makuabob)