I have cPanel on two other servers and File Manager is useful. But using DreamHosts Control Panel together with an FTP client like cuteftp, smartftp or filezilla broadens your horizons and increases your knowledge.
cPanel is a licensed system that you pay for continually, and who knows if it will continue forever.
The problem I find with File Manager is that it is slow and requires so many screen redraws all the time. It is fine for working with single files but when you have a complex site or need to upload a few hundred files quickly it is a real bind working with File Manager. With an FTP client you can drag and drop in one swoop.
It really is best to widen your scope rather than focus on just a small section.