While drilling is generally considered a 'roughing' operation, technology, tool materials & coatings, and machine spindles have improved to the point where drilled holes are generally very accurate. Reaming a hole is still the preferred method for finishing a close tolerance hole. Unlike drills, reamers require a previously drilled hole, bringing it to exact size and with a greatly improved surface finish. Reamers are constructed from high speed steel, cobalt-enhanced high speed steel, solid carbide, or even brazed-on carbide tipped cutting edges. They come in an infinite number of sizes.
Contrary to belief, a reamer will never "straighten-out" a crooked hole, nor will a reamer correct the positional accuracy of the hole. Instead, it will follow the existing path and location of the drilled hole. While the machine's spindle speed remains close to the same as a drilling operation, the feedrate is usually increased 20-50%.