Once you acquire a customer through an affiliate, you can then market directly to that customer going forward. It’s important to figure out the lifetime value of your customer as that can also help you decide what commission to pay. With this information you can decide if your acquisition costs are correct or you may decide to be more aggressive with payouts to get those customers in the door.
It also shows that you need substantial traffic to make much money through advertising. At a CPM Of £10 with 2 ad units on the site, you would make just £4,000 per month even with a million page views per month for which you serve paid ads to 20% of the audience. Set this to 100% if you are selling all your ad inventory, as for example through Google Adsense.