How tight should a cable clamp be?
You want to tighten the screws so that the cable's outer insulation is just compressed a bit which should leave you with the wire unable to move in or out of the box unless you apply a lot of pressure.
You do not want to compress it so much that the inner insulation is compressed or the wire itself is deformed.
Yes, the tendency is to overtighten these.  My rule-of-thumb is tighten gently and check if the wire can move.  If it does, tighten a bit more until you get it right.
You CANNOT &quot;undamage&quot; a wire once it's been damaged so proceed carefully.