If Gmail allowed users to sort messages by file size and delete them, would it make Gmail faster?

I think not. For me, the point is the same as ask people to delete webpages in order to accelerate Google Search. Google focus is on building performant indexes for billions of webpages, and they know what they do on this subject. Moreover, while one can be happy to be able to free some space on his account, for its own use, it can be difficult for Google to start asking people to delete their personal messages, as it always promoted content creation. I think Google should focus on making latest messages as near as possible to the user, and keep old ones on low speed storage for example. And it is what they do, as when you perform a query, usually you can't go directly to the oldest message matching with the query. And yes, a lot of people think Gmail goes slower.

The key point here is: Why Gmail does not allow sorting by attachment size? I can understand that content is needed for Gmail business model but we all know that long time ago, big file presentations are no use today (job changes, technological obsolescence, etc.). One could thinks that Google wants us to keep those large files just to be able to charge for the extra storage capacity but I doubt it. On the other hand, how many Gmail accounts are filled over 50% of its free capacity? I guess a smaller fraction. This leads me to answer the initial question saying: No. There will be a limited impact in speed if users are allowed to sort emails by attachment size and then procceed to delete the biggest ones.

I agree with David slthough this would actually be a good option for those who keep their Gmail offline as well. Off course you can do this via Outlook or a similar mail application however you need to drag these to the recycled bin in stead of pressing the usual DEL button. Another question is whether people will be bothered cleaning their mailbox altogether. What would be the performance increase when users delete about 5% of their mailbox size and how much storage capacity would google gain with that. Finally it could be an environmental benefit, less data means less storage and less systems, less power. Not the most obvious, I agree. And yes, a lot of people will believe Gmail will be quicker when they have a smaller mailbox.