Win-win-win. The advertiser wins because they only pay when a purchase is made (as opposed to the shotgun approach of paying to advertise to the masses and waiting for a small percentage to actually buy). The affiliate wins because they make money while providing helpful advice. The customer wins because they get a trusted recommendation for something they might not otherwise have known about.
The truth is much more complicated. It’s true that affiliate programs can be sources of phantom revenue and off-brand promotion. But managed properly, they can also make up 5-15 percent of online revenue and have an ROI among the highest of any online channel. CMOs are realizing that affiliate marketing can be an important part of their arsenal and are integrating the channel into their overall marketing strategies.
What are the terms of the program? Is there anything I need to be aware of that would make a program not worth it for me. For example, Amazon Associates does not allow you to put your affiliate links in emails. If your main method of communication with your audience is via email, Amazon might not be a good fit for you. Wayfair, for example, does not allow their affiliates to post affiliate links on Pinterest or any other social media site. If that’s a strategy you rely on, Wayfair might not be a good fit for you.
Affiliate marketing is also called "performance marketing", in reference to how sales employees are typically being compensated. Such employees are typically paid a commission for each sale they close, and sometimes are paid performance incentives for exceeding objectives. Affiliates are not employed by the advertiser whose products or services they promote, but the compensation models applied to affiliate marketing are very similar to the ones used for people in the advertisers' internal sales department.