Unfinished kitchen cabinets are a great choice in several situations:
These cabinets in general are face-frame construction, with hardwood face frames and plywood or MDF panels. They are intended for you to finish them yourself with paint or stain and clear coating. Generally, they come fully assembled.
Unfinished cabinets are fully assembled, but the wood used in the construction is raw and ready for you to paint or stain. Often, the interior is already finished with clear finish (not paint or stain) and you just have to do your own custom finishing to the outside. Unfinished cabinets are usually of face-frame construction.
RTA cabinets are normally completely finished, but they come in pieces, flat-packed in a box so they are easy to pack into your vehicle or have shipped. All the pieces are cut to exact size and shape and pre-drilled for fasteners, and normally the special fasteners are included in the package. RTA cabinets are usually of frameless construction.