@SuperTaliaDX
It’s a fair question. It functionally makes a difference primarily within 1) accessibility and 2) machine interpretation.
In the case of accessibility, the correct heading hierarchy makes it easier to navigate content and understand how different parts of a page relate to each other. With missing or misplaced headings the content becomes more confusing to read with a screen reader*. Jumping between, and listing, the headings of a page are common ways of navigating.
Similary, if machine interpretation is used to determine for example main, supporting and related content it can help pull relevant content to respond to questions and infer importance of one piece of content over another.
One very simple and common example would be an automated table of contents to jump to different sections of a page.
*(The use of a screen reader is of course also an example of machine interpretation)