Non profits and public research bodies only. In other words, cash-strapped researchers, funded by donations and grants from charities and so on. They can't afford much, and sparing them the cost of a supercomputer really does free up money for more important things.
Further, all results are released to the public domain when the project is complete.
If you follow the WCG guidelines and only crunch during the normal times your computer is on, then the additional electricity cost is so small it's laughable. Of course, running 24/7 will cost a fair bit more. |