Paul, not that many relais can shut down a robot on full pelt. Not without suffering any damage.

Combine that fact with the fail safe function, and you have a recepy for another power on led discusion.

Project One and II had the same failsafe setup, but used the 1 kg heavy Albright SW8024V b for main cut off.
The pricetag and the weight are prohibitive for a thoroughbread heavy.