Since you get the content to your e-mail, doesn't it mean that the readers never see your ads, therefore they never get to click on them? Doesn't that mean email subscriptions are bad for your revenue?
If you do it the right way it works really well. I'm sure you heard the saying a million times "The money is in the list" and it's true. I'm not an expert email marketer myself but from what I've learned so far, you want to give your prospect something of great value for free. Something that you COULD charge for but you're not. This builds trust with you. Then you want to continue to build a relationship with your list, don't just try to sell them shit all the time or they won't buy it and will unsubscribe. You're more likely to close the deal with someone who knows you and trusts you rather than someone they just met so to speak. Also, the list allows you to potentially sell to them over and over again. Not everyone buys on the first time too so you have the chance to get them later with your affiliate link. Hope this helps.