When you open For You, this is the thing that builds the list of tweets on screen.
You tap the tab. Nothing was waiting in a drawer. Home Mixer starts a new request.
It asks the others for posts, throws out the ones that cannot be shown, turns the rest into a score, keeps about 35, then slots ads and “who to follow” into the gaps.
It does not decide if a tweet is good. That is Phoenix. It does not remember your timeline. Next refresh = a new page.
Without Home Mixer, there is no For You. The other names only exist because this one calls them.
More: A new page every time.