Grouping images into a stack helps to keep your image library organised and neat.
Another use case in addition to what I mentioned above would be when shooting bursts, say at an event or wildlife images where you will probably use one image but want to keep the others for future use or a different use.
And I usually group my timelapse images into a stack as well, who needs a few thousand thumbnails of the same scene cluttering up their view?
So, that's how simple it is to group images into a stack in Adobe Lightroom, to keep your image library better organised just as with my images of the majestic Mourne Mountains in County Down here.