Sean, the blades have to be able to swing back when they hit something, and they have to be able to swing out again just due to centrifugal force. The need to be able to swing out again is the reason to keep them from getting so bound up with grass fibre and mud that they are more or less stuck. So yes, it is useful to keep track of them: check occasionally that you can swing them back, then swing them out again, with your hand. Be careful of course: always remove the sparkplug lead before you put your hand under the mower, and wear a decent leather glove when you try to move the blade - it has (or should have) a sharp edge.
