Stream Display Ads, Preroll and Chosen ads, what is the deal?

So, I have the qualifications to start running ads, and while I know I’m not successful enough to confidently start plopping ads down, I saw that Stream Display ads were a possible way to advertise and i read it. Could someone explain to me the positives or benefits of it? It doesn’t directly support the revenue like prerolls or placed ads, so is it free ad space because I’m nice? Like what is the benefit for the streamer is?