The response you got on stackoverflow to your question is typical of the adversarial (argumentative) nature of the site.
Some of the users with a high reputation are just totally obnoxious and the user ‘vadian’ is typical of that. His way is to say, "
DispatchGroup makes no sense in the context of a single asynchronous task" rather than include an explanation as to why he has that view. Totally unhelpful.
That said, I have no insight into how a DispatchGroup is used other than what the Apple Documentation describes.
vadian is saying is that the task you have is effectively a single asynchronous task so placing that in a DispatchGroup is no advantage since you are not dealing with multiple tasks that need to be completed as a prerequisite to some other activity.
This is an article from Donny Wals on DispatchGroup which may help you understand their use.