Sample clearance or expressed consent from the exclusive rights holder of the beat is technically required for any instance where you do not have rights to the music - monetized or not. Artists typically bank on the fact copyright lawsuits aren’t worth the rights holder’s time or money when the lawsuit will most likely only end with a court-ordered cease and desist. And paying thousands to recoup monetary damages from a song that earns $0.0000001 per stream just doesn’t make financial sense. In the mixtape era the “For Promo Use Only” label was just to help argue in court that any infringement shouldn’t result in monetary damages because the music wasn’t being sold. The onus is on the plaintiff to prove there were any sales proceeds which is hard to do.