Is that the reason why pixel tracking is used because other requests might be cached? When viewing a page, the browser client may just pull the page from cache

Is that the reason why pixel tracking is used because other requests might be cached? When viewing a page, the browser client may just pull the page from cache and not make a request to the server? A 1x1 gif is small, static, and downloaded asynchronously and makes a negligible impact both client and server side.