The system of checking in Escrima/Arnis differentiates from the standard chi sao hands of many chinese styles (Kung Fu, Wing Chun, Tai Chi, etc) in that it is based off of a weapons fighting style. Its roots and principles were built with the reference that your opponent would be armed (with a stick, knife, sword, etc) when you're attacked. This is the reason why a lot of subtle footwork is incorporated during the defense of attacks (it moves your body completely away from the path of attack while you defend with own weapon and check with your free hand). In regards to chi sao, the practices were done with an unarmed reference in mind and could be practiced with static footwork.
Funny thing about this is that I've spent a bit of time over the last few months looking into the history of the Fillipino martial arts and we've been going through a lot of trapping and disarming techniques at my classes lately, so a lot of the why's and wherefore's on this subject is very fresh in my mind. I could probably go in for a while about this. I will say this, to be able to get really good at this takes a long while. However, even just incorporating the bits I've filed away in my mind, it can frustrate the hell out of an opponent.
Bruce Lee was taught the Fillipino martial arts by Dan Inosanto, and he incorporated the checking systems of Escrima with those he had learned from the styles of Kung Fu he already knew. As a result, many of those that sparred with him have openly stated that he had this uncanny knack of defending in a way that left them totally defenseless (Chuck Norris had actually said this about Lee in an old issue of Black Belt magazine). His trapping and checking systems actually progressed into the budding grappling skills he wanted to incorporate into JKD. Unfortunately, he never got that far.
It doesn't matter if you agree or disagree
... As long as I don't bore you and I spark a moment of thought, my goal is achieved
Queng leon queng tigre ecu tacacut, queca pa? - Pampangan Mandarigma Motto