From the Orbit@Home project boards:

Orbit@home is a project based on BOINC and ORSA, monitoring the orbit of all the asteroids passing near the Earth. Every time a new asteroid is discovered or re-observed, the orbit of the asteroid is updated and propagated in future to check for possible impacts with the Earth.

As bigger and better telescopes are built, the number of orbits to update every day increases, so more computing power is needed in order to do it. It is at this point that the distributed computing philosophy enters and helps doing the work. The basic idea is the following: each different client can work with the data relative to a single asteroid, because there is no correlation between asteroids (excluding extremely rare cases, like asteroid-asteroid impact or gravitational perturbation; both these cases can be handled in an improved version of orbit@home). If the number of clients available is greater than the number of orbits to update (times a redundancy factor), it is possible in principle to update all the orbits in the same time needed by a single computer to update a single orbit. This is what makes the orbit@home project so appealing.