even with low click rates, say 1 percent. if 1000 people visit that site a day, then 10people look at your site each day, some of these might like what they find and come back, you can gain a visitor base much easier with advertising
If you don't advertise your site, then you will not get many visitors. When I first started my website back in 04-05 I didn't advertise, and the only visitors I got where my friends. Now links to my site are in all my posts, and I use the x10Exchnge banner exchange and I get around 150 unique visitors a month.