I just want to correct people on the notion of "Free" traffic. Nothing is free in this world, especially not traffic. While I would not use traffic services that usually send you worthless traffic, there are a lot of ppc traffic sources out there that can deliver you highly targeted and interested traffic. Depending on your site, this can be amazingly cost effective. People get scared off because they are paying per visitor, but the results can be instant. If you are building a community it can work very well as you pay once to get people to stick around for a long time.

Building traffic naturally can take a lot of your time, energy and even money. All the time you spend building your site, getting links to your site, and the rest uses your time and your money. There is a very real cost that people tend to ignore, and often people do not place a high enough value on their own time.

I definately think that going after natural traffic is extremely worthwhile, I just think most people do not properly analyze the REAL cost of this traffic and give it an extreme level of preference over paid traffic that it does not really deserve.

well for a new site i think its better to have a purchased traffic or just link building so to get traffic, because if you invest huge money with PPC for a new site maye be you ROI affects?

Actually do both. The nice think about serp traffic is it can keep on giving without any ongoing work or flow. However, the best scenario is to use both.

I think the strategy would depend heavily on the type of site you are servicing. Click monkey type things are just a temporary thing and can't really generate the right kind of traffic. If you work hard on SEO the payoff is relevant traffic, not just traffic.