I expect this is essentially the same problem that people deal with on the Mamiya TLR lenses.
It is easy to accidentally bump the selector to M, even if you only shoot (X-synch) electronic flash.
And you will never notice that you have done so, until after you get back your rolls of film without any of the expected flash exposures.
Particularly disastrous if you shoot weddings.
So it is really handy to be able to ensure that that lever stays on "X".