Since most major countries have by now issued from 1,000 to 6,000 types of stamps, it usually difficult for even a single-country collector to remember what is still missing from a collection. Still, most stamps are cheap, and collectors frequently get started by acquiring one or more existing collections, which will include most of the common stamps. Then the problem is to get stamps to "fill the holes"; only a handful of dealers will have a complete stock, and so the want list may take on a life of its own as the collector carries it to stamp shows, mail copies to out-of-town dealers, and so forth, gradually crossing off entries as they are located and purchased.
Topical stamp collectors will also use want lists in their search for stamps that relate to a particular subject.
Specialist collectors may have a want list with a rather different character; instead of looking for one of each major type, they are looking for particular color shades, particular postal markings, uses in particular locations, and so forth. Often these items are intended to become part of an exhibit entered into competition at shows; they may not be particularly rare, but even so it may take years of combing to pick them out of the mass of surviving postal material.