Master: If that is OFF you know your panel is dead, you cant talk to anyone,
The check of the master includes the alternator switch is in the on position, most singles have the old split switch. Not too much trouble if just landing as the battery will last, but on circuits or a T & G during a navex could run the battery dry. Running a battery out on retractable aircraft can be interesting, i know of two aircraft that had gear collapses during roll out because the alternators were never switched on. With a flat battery a manual extention was required and no indicators were available to confimirm the down and locked indication. Had some sort of checklist been adhered to properly both occurances would never have happened.
Mags: Never seen one vibrated off before but someone probably has, but if you were tought to do a proper mag check you could not accidently leave it on one or none, because you would have done it at cruise power and LOP.....because that is the only proper mag check you can do.....END OF STORY!
I have seen individual mags switched off instead of pumps or lights in certain twins when hands were operating without looking. Also had a student switch the mags both off doing this check on downwind (in a single), when it went silent it did not even occur to him why.
I also know of at least one accident where a student turned the fuel off on downwind instead of changing tanks and another where the park brake was set instead of checked off.
Have to agree with the mixture setting for descent and landing, most turbocharged models recommend leaning the mixture to keep a minimum egt during this phase.
Good check systems will catch human errors/slips/mistakes.
As long as the checks are carried out as intended.