Traffic exchange is bad for your site due to these audiences are not organic or may be they not interest in your content.
so if they leave your site in less than 8 second is count as a 100% bounce rate. But it some time depend on types of site that you are exchanging traffic,
If they are related to your content It's good for you and it's also increase your Alexa rank.
In this case Google search engine may ban your site so don't exchanging your traffic always try to make more and more organic visitor.
Traffic exchange occurs due to link exchange,it is a method of building backlinks for your site.
But traffic exchange is useful if and only if you build backlinks on the websites which is related to your niche,otherwise it doesn't help you,because if readers doesn't get the required information they leave your site without investing time to see other web pages of your website.
If order to do traffic exchange you need to create account on traffic exchange website. You can buy traffic (for example you pay $1 for 500 visits). If you do not want to spend money, you can click ads available on traffic exchange and use that credits to buy traffic for your website.
If you want to traffic exchange then you have to perform some task :-
List out back link building websites and their emails that best match with with your website category . Then you have to task send requesting email to website admin for creating link of your website . Many of them create link free of cost and some of them demand some annual fee.
If you have a newbie website or a website that has just launched can be the best suitable idea for traffic exchange. This will give a sudden boost to your new website and make a good online presence.
However, it will be hard to maintain this graph of traffic as you will always want some real traffic of the niche customers.