Whenever one owns an aquarium, one of his/her main goal is to keep a lot of fishes in there and make them grow, just like having one’s own babies but in the form of fishes. If you intend to just keep them without doing anything else, then your intention is useless. Just like humans, fishes need oxygen to stay alive. And their oxygen is supplied through the use of aquarium air pump. It is a device that provides air to the tank under low pressure; it keeps your fishes alive for a long time. Also, one of it purposes is to keep the water of the tank moving (including the ornaments to make them move like corals) to resemble the water movement of the ocean or the sea.
Other tank owners may disregard an aquarium air pump since for them it is just another added cost. If they do not plan to keep one, then they should not even plan to keep an aquarium either. Aquarium air pump provides oxygen to the fishes through agitation and not directly. It makes the water of the tank move and form rising bubbles, and through that movement, oxygen is produced and used by the fishes. It is important to keep the water moving so as to prevent the growth of unnecessary organisms and remove any form of growing algae. Moving water spells cleaner tank.
Some aquarium supplies coordinate with tank filters like the protein skimmers, sponge filters, etc. Since these filters are in need of air in order for them to work. Without the air pump, the filter is useless.