In fact, considering the raging ego and arrogance that Strange showcased right at the start of the film, he probably used it to resurrect the Ancient One, fix London, his hands and maybe even Quicksilver and the people of Sokovia from Avengers: Age Of Ultron.
When it comes to how Doctor Strange actually concluded, How It Should Have Ended suggests that Strange’s flirtation with the time-loop, and the lack of immediate consequences, probably didn’t stop with his interaction with Dormammu.
That tool could become very useful when Marvel decided to reboot their Cinematic Universe down the line.
Doctor Strange Movie CLIP - Sanctum Battle (2016) - Benedict Cumberbatch Movie