We should take refuge in the fact that very crude systems can accomplish an awful lot. Elegant capabilities are nice, but often unnecessary. -George Devol, Inventer of the the Unimate Robotic Arm.
This piece may be a little deep for most hobby roboticists, but it will be of great interest to some. If for example you're just interested in making small toys that run around your desktop following a line or avoiding obstacles then you can probably ignore it.