At times, when u try to drag and drop a field it doesn't get dropped to the specific place so you have to drag that field again and drop it. This happens rarely but does happen. Any user who at a crunch time has to prepare a report can face this issue when things are done in a hurry. This double click functionality can help save time during that crucial period.All the users can be benefitted and modules across the product can be benefitted with this functionality.
Both the functionalities can coexist!!