Probably not, but we could make him believe that off-topic discussions make the site slower.
(well, it does in a way, but it is not really noticeable on short term)

So off-topic chats aren't that much of a problem for you? Because sometimes you've seemed slightly exasperated (I don't blame you because often people just don't listen) and said things like "Are you kidding me, King of Off-Topic?" and last time you said "This has got to stop".

They fill the database. The biggest the database is, the slowest the site is.
For example the increase of database size force the site to move to a dedicated server.
It is not a major problem now, but after a few years it may become one, and it is difficult to delete useless discussion afterwards.
Hence why I try to stop these when they start, and try to clean these directly.

Isn't it a strain on the server with everyone refreshing to see the latest comments? Maybe if they could be made to appear automatically that would reduce some traffic.

The "last comments" page is not very heavy, I could optimize it.
The heaviest is the vehicle search page. Especially when it returns a lot of pages of results (even if only one page is displayed at a time). Hence why I suspect Google indexing.

opps.. I thought the problem was my connection. I see. Yes, from some weeks, some times the site works fast and, only few seconds later, it's too slow. If you are editing IDs, it becomes frustrating.

Site is being annoying slow it has to be said. It doesn't help that whenever you edit comments/vehicle info, it has to take to you to a page telling you it's been updated successfully.

What seems to slow down the site is the repeated searches made in comments, for very short words (hence a lot of result pages), e.g. "st", "b", "si", etc.
Probably that the search url of these ended somewhere, and is then taken by Google for indexing.
I'll block the comment search for non-registered members.

Done.
If you notice again such slow downs do not hesitate to report them. Now that I found again where I have to check the cause, I'll be able to more easily find what cause them.

(note for myself if it is in a long time and I forget again: check /var/log/mysql-slow.log)