Ok i may have went about the post wrong
meth/h2o cools the charged air yes and because of the methanol in the mix adds octane value but the injection to the turbo also can and has damaged turbos as water impacting the turbo rotor/blades pits and can start corrosion of the blades.
the nitrous comment was a side comment as lots of people got it wrong with their shots and overheated the engines.