MDF is medium density fiberboard and can be used in a variety of areas. I would say one of the most common places are units that you want to paint and repaint in time. This will save you buying a new unit if you change the colour of the room. The unit can be painted to match any changes made unlike MFC which would be harder to do.
MFC is Melamine faced chipboard. This can come in a wide variety of colours from plain white, cream or ivory to your wood grain effects like Oak, Walnut and Beech. Wood grain effect units really finish off the kitchen units so that they blend into the kitchen once you are getting the same wood grain doors or worktops. Wood grain kitchen units also add some class to hand painted kitchens with the contrast working very well.