Allows for greater backwards compatibility as well as support for different resolutions, unreleased games such as Goldeneye 007 XBLA (the cancelled remaster from 2007-2008), game removed from the Marketplace (Daytona USA HD for example), etc..
It’s adding another layer of value to owning an Xbox Series console at this point, for $250 a Series S that can play consoles from 360 and back at 1440p/4K and 60fps is an incredible value that’s making me consider getting one. Not to mention next gen support.