Most of the newbie affiliate marketers start with their affiliate business with free traffic. But due to the lack of quality, the conversion rates are too low. They didn't get the targeted result that is why the profit margin will go low. Beside most of the free traffic are come from spam marketing which means you need to research very well if you want to live your affiliate link. On the other hand paid traffic is targeted and well converting. You'll get maximum ROI if you follow some strategies, for example: collect leads, follow up email, targeting, etc. It's like a business the actual affiliate marketing. Need to do proper invest and get profit. So, in my opinion, there are no option then paid traffic in affiliate marketing.