As an affiliate marketer, you help product owners who has an affiliate program to sell their products. Basically, you sign up to their affiliate program, and they will provide you with your affiliate link. Once you have that link, you can place it on your website, social media or wherever. As Long as you are speaking to the right audience, people who are in your niche (people who are interested in what you promote), and they buy a product through your affiliate link, you will earn a commission.
In the long-term, it affects your versatility, functionality, and, of course, your brand. In the short term, it can certainly add/take away a lot of headaches. That said, just like choosing a physical house or office, there is no such thing as an absolute “best” or “top” choice. There’s only the right choice relative to your goals, experience, and circumstances.