"if it's free then you are the product" is an important thing to remember when it comes to websites and apps. you don't have to pay to use facebook, but other companies are paying facebook for data and advertising. there is no company under capitalism that can maintain itself purely on generosity towards users. this business model is also how many modern tech monopolies are able to evade antitrust laws.
also, "if its free then you are the product" doesnt mean that just because you buy a service/product, you are safe from data harvesting. i have seen people use this phrase to justify the pricetag on a freemium service (aka the paid tier of an otherwise free website) and believe that they have protected themselves for $5 a month. you might not be getting served ads, but ads are not the only form of invasive data practice that services make their money on.
also true‼️