I'm used to having Ensim add both domain.com and www.domain.com as A records. I notice that cPanel adds www. as a CNAME instead of an A record. Why? Are there advantages and disadvantages to doing it one way or the other?

By adding a C-name it "follows" the IP of the A record it is pointing too. This can be very handy if you create a lot of virtual hosts. If you ever need to change your IP you just change your A record and all the C-names follow suit. If they are all A records each one must be changed. Just don't point your mx records to a C-name. MX records and C-names must point to A records.

A records are faster...

Cnames require another lookup.

Has anyone modified cpanel so it adds an A record instead of a CNAME for the www. entry then for speed?

As far as chaning IP's in the future, I would hope the liklihood of that happening is pretty small, and even if it did I would probably just run an ssh command to find and replace within all the named db files at once, so I don't see it making a difference whether the IP occurred once or twice per dns record...

Are there any other reasons CPANEL by default makes www. a CNAME rather than an A record?