Yes, you are missing something.
You are the product.
By using these services, your beliefs, habits, work, and by extension you yourself, are slowly being turned into a product for consumption by, at best, profiteering business executives, and at worst, totalitarian regimes.
Does facebook want you to find and actually spend time with people? No, they want you hooked on their website endlessly posting cat pictures and looking at cat pictures from your "friends". By doing this, they make you lonely and isolate you from actual social contact; there's an entire generation of kids who think socialization is facebook. Facebook is loneliness and isolation and when they have you there, on facebook, isolated, they own you.
Integrate your Facebook with Spotify? Someone pays spottily to run subversive, politically motivated songs. Who do you talk about that for reference? To know if the politics or history you are being sold are factual.
Integrate your Facebook with Uber? Uber now knows your approximate income and how gullible you are, and will charge you a consummate rate.
Integrate your Facebook with your New york times subscription? All of the MSM outlets use parametric targeting of readers to display articles to them think they will identify with. If someone pays them advertise to passionate democrats in order to get them to donate, chances are, you will see a never-ending news "feed" (Love how they call this a feed, like a cattle feed) of tabloid news which provides you with all kinds of "calls to action" in order to donate. You'll see stories on how chocolate cures cancer, then an ad from nestle. The more information they have on you, the more precise and intense the targeting.
And you won't know, you can't know, because engaging in that degree of paranoia is crazy.
What do you get by opting out completely?
Advertising works by making you unhappy, by manipulating you to be unhappy, by whispering terrible and horrible things in your ear and hoping you buy a lifetime subscription of unhappiness. It tells young, beautiful women they need makeup in order to be beautiful. It tells ingenious IT geeks they aren't good enough without knowing framework X or having product Y. It tells fat people to buy dieting products that never work, that can't work, because if they were to cure the problem, they couldn't ever be sold another approach. Go search google for weight loss right now; How useful is ANY of that information to someone who wants to lose weight? The observation being, google is providing you with nothing, absolutely nothing, because you_are_the_product.
While you are ingesting advertising, you will never be content. You will never be fulfilled. And worse, the more time you spend in the bubble, the more of what and who you are will be configured to be that unhappy, totally messed up amalgamation people the big businesses wanted you to be, and the longer it will take to de-consumerize.
This is what psychological warfare has become; what the studies and sciences of psychographics, psychovisuals, psychoaudio, public relations, communication and marketing has become.
If you opt out, you retain your freedom to think for yourself, act for yourself, and be yourself. You retain your ability to be content and happy. You get to have real friends. You no longer exist in the 7th circle of hell.