[intellec7]

Another reason why I isn't always desired to be reset once error=0 is in the case where you have a two wheeled platform that you want to travel in one line.

Ensuring that both wheels turn the same amount is not enough to ensure that the robot goes in ONE line, it just ensures that the orientation of the robot is the same.

To have a robot that goes straight, the wheels have to turn the same amount in the same period, I can "remember" all the differences between wheel positions and then make the proper corrections.

There is an algorithm that works just like this in "Mobile Robots from Inspiration to Implementation"

Also, for a balancing robot, lower COG is not necessarily better. A higher COG gives the robot more rotational inertia and therefore harder to throw off balance.