Do you mean the pros and cons of joining AdSense in general or from a tax perspective? Well, one big pro is that you can earn revenue from your site without having to have any products to sell. A drawback is that you may drive traffic away from your website. Some people suggest not putting ads on "important" sales pages so they don't distract.
As far as taxes, it is my understanding that if you don't make at least $400, you won't be getting a tax (1099 form) from Google. Here's a site with some info about it.
http://www.adsensetaxes.com/
Bottom line: You should ask a local tax professional for questions. A lot of internet info may be outdated or incorrect. Or you can check the irs.gov website for specific amounts and rules.