One of my flatmates did it for a while to pad his unemployment money. It's probably not that normal to do, but anywhere else I've lived this would be unthinkable.
You can make a lot of money with it if you do it in areas where the homeless rate is low. Especially in the first years when it wasn't that common, I knew someone who made more than 40€ per hour with a good strategy of where to go. Best thing about it is that it's tax free and legal.