You get amazing features like: background play (which is more of an annoyance), remember where i left off (which doesnt work whatsoever, even 5 years after it was first released), download video's to watch offline (you need to remember to download them first or hope that YouTube's recommendation algoritm didnt pick videos you've already wachted) oh, and you can get a slightly higher bitrate for 1080p. So basically it loses all value.
The other replies are incorrect, the lower tier premium actually has no ads on most videos. When you subscribe, they explicitly let you know music videos will play ads, probably so this plan is not eating away profits of YouTube music.
they get even more revenue from other peoples contributions.
thats the whole point not more, not less.
so there is no point for "you" to pay them anything.
did you as a "premium customer" thought to be "the customer"? really? remember how little you personally pay for the service. it is mainly the ad companies who are youtubes "customers". when you pay them for something, you only increase yt's revenue, not more, not less, but you are not "the customer", you are the product ;-)