If you already have a printer why bother? Just buy a cheap scanner. It is my experience that home users only ever use a scanner about 1% of all PC usage time. So why spend big money on one if your not gonna get the use (like a DTP, or Web Designer would?).

To answer your question though, yes they are good for many reasons. They save space, one unit only.

You get a Printer, Scanner, Photocopier, Fax (providing you have the software) and the quality and price these days is great.