The danger with any of the mag "dead checks" is switching off and then not immediately switching them back on. Even a slight delay will result in a backfire and probable damage to the muffler and/or other parts of the exhaust system.
IMHO, it is more important to do the dead cut at a low RPM, than to do it very briefly.
My POH (IO540-C4) makes that fairly clear.
Another thing is high altitude mag checks
Especially with the mixture leaned
Very desirable to check out the ignition system. But needs to be done with care - if you get any issue you have to
close the throttle before returning the key to the BOTH position otherwise you again risk exhaust damage, but more seriously than on the ground checks which are done at a very low power setting.