What is the Query Manager for?

I feel daft asking this but could you tell me what the AC Query Manager is for?

If I click on ‘App’ in the App Structure, I can define the Query Params there. Having added a variable, this is available in other actions. So I can’t see any difference between having the Query Manager action in my structure or not having it.

Does it do something else I’m not aware of? Or is it just to make the query variables easier to access so not actually needed?