Two benefits: (1) you have less liability if you don't know their passwords, and (2) they can design passwords that they can remember.

And one drawback: some people are likely to write it down rather than change it. If you can force them to change it, that's great. But if not, there is some merit to generating pronounceable passwords.

BTW, your reason (1) doesn't necessarily apply at all. Generating a password for a user doesn't imply keeping a record of it.

-sauoq
"My two cents aren't worth a dime.";