I am glad this is mentioned since it is so helpful for screen reader use. It is very handy when using a screen reader to instantly jump to the body of the text with the most semantically relevant info. (So being able to skip certain headers, unnecessary info, navigation bars, etc.) Yes, you can also do this simply by jumping between landmarks but having the ability to instantly jump to the main content reduces friction for non-visual use or helps less-tech literate users who just want to get the main content read.

I think this survey is useful for looking at other preferences of screen reader users (even if it is just one survey) https://webaim.org/projects/screenreadersurvey/