First, if you’re planning to use it as a photocopier, it’s going to cost you considerably more than having copies made at your local print shop. Where you might spend 5 to 10 cents a copy at a print shop, doing your own could cost anywhere up to $1.00 a page on a multifunction printer.
They’re great for convenience when you need a quick copy, but you wouldn’t want to do any kind of volume on them.
Another thing to consider is the quality of the various components. For example, the scanner may not be as high resolution as some stand-alone models.
If you’re planning to scan old photographs or negatives and want the highest possible resolution, you probably won’t get quite as good a result from a multifunction printer/scanner as you would from a dedicated scanner.
The same goes for the printing capabilities. You can get standalone printers that will print at higher resolutions or on larger paper than most multifunction units.
The final thing to consider is that if you ever have a problem with your multifunction printer, you’ll lose your scanner, copier, printer and possibly fax while it’s getting repaired. Having separate units means you would only be without one of them if you ever need repairs done.
If your needs are relatively basic, however, a multifunction is a great choice. You can get all the same functions as having 3 or 4 separate machines, for less money and in a lot less space.