Every comment here is missing a crucial point. The data is used to identify what kind of person you are and then manipulate you based on that. It’s not just to target specific ads to you. It is to control how you behave in any way that will profit them. An example of what has been done is to identify democrats that were unlikely to be convinced to switch to republican, so instead they targeted them with content that would get them to not vote at all.
Interest based ads that everyone who has connected to the same wifi as you will now see. And it’s not just interest based ads. They will use this to calculate your whole personality and manipulate you and others based on that.