Earth is located in Sector 2814, and while Green Lantern Corps could easily follow in the previous Green Lantern movie’s footsteps and keep the main action based on our world, it would be better if the human Lanterns instead ventured out to other worlds, visited different alien civilizations, etc. This then paves the way for other cosmic-focused DCEU movies to be released, such as one based on Jack Kirby’s Fourth World mythology.
The DC universe is divided into 3600 sectors, and in the modern era, at least two Green Lanterns are charged with protecting a sector.
DC has published plenty of stories over the decades that aren’t set on Earth, and the Green Lantern Corps movie can serve as a great way to fully delve into these other intergalactic corners, just like Guardians of the Galaxy did for the MCU.
So far the only major ways the DCEU has delved into DC Comics’ cosmic realm is by Man of Steel briefly visiting Krypton and Justice League having Steppenwolf and his Parademon army invade Earth (twice), but this is just the tip of the iceberg.