For use nothing, for installing something.
I have a rasp lying down and holding my personal photo gallery, for example. It doesn’t waste electricity too much and I don’t expose my laptop to every other users. Because I’m using already Discourse as a private notebook I could use raspberry for that because I don’t have need to access it from outside world and at same time I could save close to 10 buck a month VPS bills.
That is one reason. Matter of choise, nothing else.