Ants come in many varieties. Most are harmless to us, and although found distasteful by many, away from the dwelling they are beneficial in as much as they aerate the soil and dispose of dead insects etc.
However, once they get into our homes, even the most harmless species are a nuisance, and because of their disease spreading capabilities need to be eradicated. We now have some very effective treatments to deal with all species of ants in most situations, even if the nest is not readily visible