I never liked this type of obfuscation.
First of all it's creating background traffic, which might not be much, but it's there. Also data caps as someone mentions above.
Second, and most importantly, it gives possible interpretations to that fake data. Imagine there is an specific combination of sites that the dataminers assume to match a type of sexuality, religion, etc. Sure, your profile will be false, but it won't be considered useless: Whoever is spying on you will take it literally because they don't know better, and will add preferences based on the fake data, instead of the opposite. For the better or for the worse.
It's like when you have your youtube suggestions based on what you actually watch, and then someone sends you a nyancat video, you open it, and suddenly your suggestions keep suggesting more nyancat or internet memes like it. Datamining seems to be additive in what it contains, it'll just add new stuff without bothering to check for conflicts, apparently.
Imagine your profile is exactly the same as before, except with random changes based on someone else's ideology. Imagine you are labeled as the wrong sexual orientation, political ideology, religion, etc. Imagine an employer buys access to that profile and discriminates you based on wrong data.