When you dont want to spend money to support an ad supported website or ap. Instead of giving money you commit click fraud to give that website more ad revenue.
1) Jack liked his linux distro so much he wanted to give back, however he didnt want to give money and had no programming skills so he clickpromoted the website instead.
2)Max was friends with Kyle. Kyle had made a website. Max went onto his website and clickpromoted Kyles website because he was trying to encourage Kyle to spend more time and effort into his website.