I keep seeing this claim. Where to sell this data and how much for example 1 million unique visitora / month worth?

User data for a single website is probably not worth much. User data for every single website a user visits in a day? A bit more. Hence, advertising networks.

It helps determine the price of the ad they are showing.

So first you need to join an ad network. Then you could be paid more for higher revenue visitors.

That's one of unsolved mysteries for me - who exactly buys that data and why? What do they do with it that is worth paying money for? Let's say you've learned I like reading sci-fi. So what? You'll serve me more relevant ads? I have an ad blocker anyway, so you won't, and even if I did not, I haven't seen an ad relevant to my interests in ages, except on the topic sites that I already visit anyway. What are they doing with it that is worth clogging all the internet and making each website 10x of size it should be? I have a nagging suspicion it's all hype and one day advertisers will wise up and this business model dies the long deserved death.

There are companies that act as data brokers for other parties and there's also companies like Nielsen which buys media consumption data in bulk. It's not just about the ads.

It's also about the way in which to split the pie. (how much should go to this creator?)

Or consumer profiling. (It seems our product is enjoyed by men in their mid 40s who like sci-fi)

Or marketing research (it seems our product sells the most in winter).

There's plenty of ways to make use of this data. That's why it's so valuable. It's not uncommon to see 7 digit contracts for high profile news/gossip outlets, for example.

> There's plenty of ways to make use of this data. That's why it's so valuable.

That's what I keep hearing. Never heard what are those ways, specifically, and where the value worth the money comes from.

> Or consumer profiling. (It seems our product is enjoyed by men in their mid 40s who like sci-fi)

OK, let's say you learned that. Let's say now you know there's more demand for beard trimmers among mid-40 males with interest in sci-fi than among teenage females with interest in Rihanna. Now what? I still fail to see what a bunch of random (and possibly entirely spurious) correlations costs in money.

> Or marketing research (it seems our product sells the most in winter).

You don't need to track me for that. You need to track your inventory. That's basic stuff every merchant having a functioning brain is already doing.

What else is the data being sold for besides advertising?

It's still all about ad revenue though.