Frequency matters, and how often you send emails can have a significant impact on your revenue and email engagement (and unsubscribe) rates. Send too much and subscribers can suffer email fatigue causing them to disengage and unsubscribe. Send too few and you lose the attention of your audience. They may even forget why they signed up leading them to unsubscribe.
One of the cool things about Google AdSense is that it's so easy to get set up. If you have a blog or website, you can sign up for a free Google AdSense Account. From there, Google will give you a unique code that you will paste onto your website. Google takes it from there, tracking your page views, traffic, and earnings on your behalf. There is no upkeep or maintenance to get this thing going, which makes it a no-brainer if you have a website already.