I've been using this kind of printers for more than six years, it's just convenient!
First of all, the output quality is good. If you buy photo-paper for it, it will really print photographic quality output! The only downside is the price of the ink and the paper, but it could be very convenient if you were asked for photographs at night for the homework of kids.
It features photocopying capability. You don't even have to turn on the computer to use this function. The output really likes photocopy in some cases. Of course, if your model is like mine which only has a roller type scanner, you could not easily make copy of thicker stuff.
Next is the fax function. Yes, it's not exactly high tech stuff, but it could be handy for some cases. Fax is still very popular!
Finally, the scanner function is not bad especially for converting your paper photographs into digital. Other functions like OCR are useful sometimes. Storing a backup copy of important document by digitalization is a nice thing too.