That may work, as long as you know to do that for each new user as well. Depending on your setup this can likely be automated via a file in a skel directory, or done via a global procmail config file.
Postfix was probably handing the mail off to procmail instead of delivering it directly, so if you disable procmail in your postfix config, it may also work that way. (Comment out the mailbox_command setting in main.cf) You do not necessarily need procmail, unless you have a specific task that requires it. It can be handy, but it's not required.