Drop off at a different VAC

Hi, I am trying to understand the drop-box system. Let's say I select the Mumbai consulate for visa processing and create my account and pay the fees. Now when selecting the drop box appointment if I select a different location, let's say the Chennai VAC, can I drop off my documents at the Mumbai VAC at the same time and date? Or does it have to be at the Chennai VAC? The website says they allow you to drop off documents at any VAC for free. But then what is the point of having these different VAC locations? Anyone can select any VAC and drop off wherever they want to. Hope the question makes sense. Thank you!