Belt sanders are a great sander for high removal of wood in order to remove imperfections or get the wood to a smooth finish fast.
Delta sanders are the tool when it comes to sanding into edges.
Orbital sanders are a general purpose sander for smoothing and removal of imperfections in wood.
Random orbital sanders are the sanders to hire when a swirl free finish is required. Normal orbital sanders create a slight swirl pattern in the wood surface, this is of little consequence on most finishes but on items such as furniture where the finish is paramount the swirls need to be removed, this is where a random orbital sander becomes the tool of choice.