I sign up as an affiliate for programs/people I am 100% behind and use myself. When asked for a recommendation for that product or service, I provide my affiliate link (openly). The income is a nice addition (at the highest, a few hundred a month), but it’s not my focus. I do see how it could be lucrative, but my primary aim is to develop my own products instead of selling for others. Depends on your business model, I reckon.