The search engines ( Google, Yahoo, Live ) are so powerful for one single motive: they HELP people in finding faster what are they looking for.
You can see for yourself, that people have money and are always looking for something ( all the time! ).
But how can I tell everybody about my new site?
It's not that easy to reach even the first page on major search engine. Actually it takes a lot of time and work to do that. And to reach the first 3 positions that is even harder!
Take in consideration that in order to promote your site you already made a happy investment ( buying this script! ).
So you have a hard work that takes time ( promoting your site ) with a limited budget. How do you do that?

Did you consider taking an employ to do some work?
How about an employ that only ask for one small check at the beginning and works for the rest of his life day and night?!
This is what Twitter plug-in does: works all the time in promoting deals, coupons or pages from you site.
Would you believe that such a plug-in can give 200.000+ clicks / month - with only affiliate network?

Let's do math: how much will you pay to get 10.000 clicks? At 0.01 cent with Adword that is 100$ ( but with a bid of 0.01$ you will NEVER reach 10.000 click on AdWords ). Still it is not for sure that anybody will buy from your site.
Now compare 100$ to the cost of the plug-in which is 75$.

You already made a profit?! That means that you are good with math. Now take in consideration the volume that Twitter plug-in gives you ( 200.000+ click! )
And there is more: not only that you spend 0$ on your ads but you also invest 0 time in doing that!