Everything, including apps.
Although, recently YouTube has been bad for me. Earlier i would almost never see ads on YouTube. I just pay Hulu more, so I've not tested that.
I just broke down to pay the $x/month for ad-free youtube. I watch a lot of streams with regular updates (Tim Pool, Keto Connect, etc). I get far more value from YouTube than I do from Hulu... that's just me though.