If you weren't already aware, Facebook is watching you. All the time. They're tracking both your activity within Facebook and elsewhere around the web, then using that intel to curate a custom profile of your "interests." Then, they use that profile to better target you with advertisements, both on Facebook and within its "Audience Network" of mobile sites and external apps.
Unless you want to start cutting a portion of your monthly paycheck to Zuck and co., being inundated with ads on Facebook is a necessary evil. The problem is, you end up getting served a bunch of crap ads that are totally irrelevant to you and your actual interests. It's all too easy to end up with a skewed profile, especially if you do a lot of random online research.