How? It is not a secret that ajax is mainly used for loading partial content from server and thus no full page reload is needed.
This is a well-known technique, but there is another point of view, which I discovered during the development of a huge media website that is always under heavy load.
Consider single article page.
- site header
- related news -on the bottom
Advantages I receive, is that when search engine crawls my article page it will not load unimportant data. Secondly, page size becomes smaller and thus page load is faster.
Third and the most important! More durability during DDoS attacks, because scroll event will not fire and thus there will not be an additional load on server, so server can handle a bit more requests before crushing :)