What do you think your computer does most of the time? For most of us, most of the time, it just sits there idly spinning its wheels.
It doesn’t have to be that way. There are many distributed computer programs, such as Seti@home, the search for alien life; Folding@home, protein research for understanding how many diseases work; and the just announced Quantum Cures project which seeks to find cures for “orphan” diseases. Most can put your PC to useful work while you’re drinking coffee or asleep in your bed.