Tracking is actually incredibly tiny bandwidth-wise. Like, fractions of a fraction of your bandwidth. Adserv is also very tiny due to modern edge server infrastructure. Ads are static content. It's already cached and likely within the same city as you. That's part of why ads tend to play perfectly and fast while the content can be slow. On the other hand, that obscure 200 sub guy ranting about why the square-headed screws inability to catch on is a giant American conspiracy to keep Canada from commercial dominance is almost certainly not locally cached. It has to come from Google's video content servers way out in silicon valley.