Modern genetics would not be possible without the humble fruit fly.
Fruit flies are also a valuable asset to scientists performing genetic research. (fruit flies and humans share 75% of those genes which cause disease. Their short lifespan is also amenable to examining changes and mutations that can occur between birth and death.)
It is relatively straightforward to mutate (disrupt or alter) fruit fly genes.
They are inexpensive to maintain in the laboratory.
(all the benefits i found are related to experiments)