Mars rovers are typically very slow. Curiosity, for example, has average speed of about 30 meters per hour.

Why is it designed so slow? Is it because of some specific power restrictions or for other reasons? What is the top reason why it is so slow?

It has more to do with the rocker bogie suspension than anything else.


  The system is designed to be used at slow speed of around 10 cm/s, so as to minimize dynamic shocks and consequential damage to the vehicle when surmounting sizable obstacles.


In exchange for moving slowly, the rover is able to climb rocks that are double the wheel diameter (normal suspension has trouble with anything over half the wheel diameter).  This is important when travelling in — literally — an alien landscape.  



(image via http://en.smath.info/forum/yaf_postst995p2_Animation-of-mechanisms.aspx)

There are other benefits that come with slow speed: better correlation between successive frames captured by its navigation cameras, more time to plan its path, and power savings.  However, without the capabilities provided by the suspension system — surmounting the obstacles present on the martian surface without getting stuck or causing damage — the other benefits are moot.
