Talk to cPanel about it

Any time we do a transfer of a client to our server we always go in and reset the bandwidth counter

Just as when we restore an older backup we also reset the bandwidth counter to whatever it was before the restoration so that they have an accurate idea of their actual usage.
Everything needed to recreate the account as-is including access logs, error logs, emails, databases, etc...
I would download a full backup every *once* in a while but make sure you download your public_html and your databases regularly. The databases are likely the most important as the rest can be recreated in most cases.
Granted this thread is a couple days old, I figured I'd still reply:
Talk to cPanel about it Any time we do a transfer of a client to our server we always go in and reset the bandwidth counter Just as when we restore an older backup we also reset the bandwidth counter to whatever it was before the restoration so that they have an accurate idea of their actual usage.
Yes, you're right that cPanel migrates the usage statistics as well - but that does not constitute a full backup for a user (as it's not usually intended). It's more of a "gotcha" with cPanel.
Everything needed to recreate the account as-is including access logs, error logs, emails, databases, etc...
E-mail's, logs, and such are all on the hard drive tied to your account (typically in your home folder) - so when I said "anything on the hard disk..." it included access logs, mail, and so forth.
I would download a full backup every *once* in a while but make sure you download your public_html and your databases regularly. The databases are likely the most important as the rest can be recreated in most cases.
While I agree a full backup is nice occasionally, I personally prefer a bare-minimum approach as it can get to become quite cumbersome otherwise. For example in my backup I don't really want access logs, I rather have the data required to restore my website as quick as possible.
The tone of this reply may seem defensive, but I think of it more as a elaboration of my previous reply and the points you pointed out.