Yes, thickness matters. Rotors must have enough meat to absorb and dissipate heat, and to maintain their structural integrity. Thin rotors are dangerous rotors that increase the risk of heat fade, cracking and failure. That is why most rotors have a "discard thickness" or "minimum machine to" specification on the casting. If you can't find it or the numbers are illegible, look up the spec in a service manual or electronic database.
