First, You got traffic and a lot of traffic without paying a dime. Some of your traffic will actually click on your ad or buy products from your site. Most importantly, it is free! (the best weapon on internet marketing Ever)
What's bad about so-called FREE traffic exchange?
They are not targeted traffic and you will have to either "work for credit" (e.g. watch their ads, click the banner) or "pay for credit" (usually more expensive than you actually buying the targeted traffic. Also,people are reading your site just to get "credits" and are not necessarily interested in your products.
Almost everybody who need to promote their website(s) have joined such services one time or the other. It's the lure of fast traffic that drives webmasters into signing up such services. But unfortunately, the quality of traffic you get from these services is inferior because it's just members who visit other's web site to get credits. If you have a web site to sell something, traffic exchange program may not be a good way to get targeted customers and boost your revenue.
However, if your product is targeting to a group of webmasters or people who sit in front of the computer all the days, traffic exchange program may be a good way for you to get targeted customers.
As I have mentioned before, you actually get "traffic" from those program and it is only a matter of fact on "HOW" you attract your customers to spend 1 minute to read your products or your web site. The beauty of traffic exchange program is that, over 90% of the people in this program are either webmasters or marketers. If you have products or service targeting this group of people, traffic exchange program will no doubt be your number 1 choice.
How to use it wisely?
As I have mentioned before, using "free traffic" to sell affiliate program and webmaster tool, such as seo tools and other online marketing program, would be a wise way. But what really bring you real cash is the "reputation" you build up among other webmasters when you use those "webmaster-targeted" program.
How do you build up your reputation? 1) Provide free content for them 2) Develop downstream using those "free tool"
Then once you have built up your reputation, chances are other webmasters who use this free tool will follow your recommendation and you will be able to make tons of cash from those webmasters (your customers).
Good program such as instantbuzz, trafficswarm and trafficg is a good way to get started if you are new to this "free" traffic exchange stuff.