"Macro" means big. Macro photography is therefore a branch of photography in which the resulting subject photographs "large" in the photo, as large as in real life or larger. For example, if the size of an ant in the photo is equal to or larger than its size in real life, that is a Macro photo.
The first use is to contemplate the beauty of the "little" things that surround us. And I say small quotes because they are small is very relative, they are only small in our eyes, and that's where the usefulness of macro photography, which is able to teach us the beauty of the subject (whether object, animal or plant) in question.
Other more objective uses are those of biological research, which is a field that owes much to Macro photography, since it has allowed us to document many studies related to many animal and plant species.
Also thanks to the macro photography it is possible to contemplate and enjoy some jewels or valuable objects whose very small size usually prevents them from being appreciated in all their detail.