In military purposes, it can be used as long-range detection to see any danger in space before it arrives Earth.
In peaceful purposes, it can be used to explore uncharted regions and areas of space without exploring them.
It appeared in 459, when Ant-Man and Janet visited the space observation facility run by Carol Danvers (later be known as Ms. Marvel) and Dr. Phillip Louson (revealed to be Captain Marvel in undercover). The observatory had detected the Kree Sentry from outer space which it got its attention. Then it went to Earth to destroy it.
Despite of Ant-Man's and Wasp's best efforts, the observatory was destroyed by the Kree Sentry.
In Captain Marvel's conversation with the Avengers about his people and the Sentry, Thor had accused him that he's in league with the Sentry, but the latter revealed that he's trying to cloak the facility so that the Sentry wouldn't have detected it, but he failed and offers to help the Avengers destroy the Sentry before it cause more destruction and harm on Earth, which the Avengers agreed his offer.