Internet growing day by day. Now so many URL are used daily. Everybody has to remember so many URLs in his daily working life which he need to use somewhere. For this either he has to remember that URL or he has to copy paste it somewhere.
If it is small URL than its easy to remember or share. But in case of long URL its became complicated to use that URL for sharing purpose.
By keep such things in mind many companies started shortening the URL like GOOGLE also started the shortening URL service.
As many people are visiting many URLs in his daily life so few company like Adf.ly start taking advantage of this and making money from this. Companies like Adf.ly also give chance to its user to earn money by shortening URLs and sharing them among their friends.