Finishing the game is worse than just stalling before the Battle of Bunker Hill forever. Once you finish the game, most factions are locked out or killed. Danse has left the Brotherhood if you sided with the BoS. There is an actual cut ending where you can finish the game as the Minutemen, but then go to the BoS and have them promote you to Sentinel for using the Minutemen as cannonfodder against the institute. There's only a small amount of extra content that happens after the end of the game, but they only consist of a few encounters. And finishing the game with the Institute doesn't open up anything new.