Practically speaking, this flag is of use for scenarios where the "Random" option does not make sense in context (e.g. Psychic, where Class determines whether or not weapons auto-fire) or it breaks a script that relies on the player retaining their class after respawn, to state an example I've seen from this older suggestion thread (which can be safely closed if this is added).
Note that this patch only disables the selecting of "Random" via the menus, so entering "Playerclass Random" from the console still works just fine. That's by design, of course.
