Purpose of this from the WCAG guidelines about text-spacing

I need help understanding this guideline about text-spacing. I'm wondering what is the purpose of these text style properties in the bulleted points. My understanding is that users should be able to override the text styles. That's what I got from reading this article. But then what is the purpose of the bullet points? I guess what I'm really confused about is the sentence "no loss of content or functionality occurs by setting all of the following and by changing no other style property".

I know there are some explanations in the Intent and Author Responsibility section but I guess I'm still confused?

In the Intent section, it says: "Each of the requirements stipulated in the SC's four bullets helps ensure text styling can be adapted by the user to suit their needs." And in the Author Responsibility section, it says: "Rather, it specifies that an author's content has the ability to be set to those metrics without loss of content or functionality." But I don't understand how these are related to users applying text styles (like enlargening the font and spacing) and ensuring that the author's content is not cut off.

Am I missing something? Am I just confused after reading this whole article?

Edit: Basically, if users will override the text style for their needs, what is the purpose of the text properties in the bullet points if some users might change it to something else?

link: https://www.w3.org/WAI/WCAG21/Understanding/text-spacing.html