Well, I have seen failed projects where the complete lack of commit sanity wasn't the cause, but a very clear sign, of what was wrong. Perfect examples are commits labelled 'no changes' (the author's way of saying 'whitespace/formatting only changes', I think) but where addition of braces in languages sensitive to that actually caused behaviour changes. And more bugs on top of the existing trainwreck.

What can be important is simply a general concept of meaningful messages

This basically. All these commit message rules, whe applied, are just another way to force the comitter to reflect on what he/she is writing (both the message and the code), whether it makes sense, and so on. I've seen so many cases where someone had problems describing in simple terms what a commit was doing and why, just because the code was, well, a mess. Forcing the author to dissect both the commit messsage and code then usually makes it very clear how to improve both.