Having a Website listed as part of results of a Google search provides three times more text than a Google AdWords (on the right hand side of the page). This means, that your opportunities to atract visitors are about three times bigger. And also, once you have attracted the visitor to your Website, you have more chances that he becomes a customer, as he has landed in your page knowing better what he would find on your Website.
A Google AdWords ad has about one third of the text one finds on a Search results link. Some customers might click it just to know more about it and not always because they want to buy your product. And this click, will cost you money in the Google AdWords program.
The advantages of being listed as part of Organic results are multiple. Not only you will not pay for every click on your link (avoiding that simple curiosity could consume your budget) but also visitors will be better informed before landing on your page.
This will be because the information they have found about your products is more extensive and has attracted them. Chances are that visitors become customers at a higher conversion rate than those coming from pay per click ads.