My reasoning is that if the two sides are indistinguishable, or there is no other way to tell which checkers have made a complete tour, then a player could easily mistake a checker which made a complete tour for one that had not and bring said checker back into the game.
I am mostly referring to the physical game.
My reasoning is that if the two sides are indistinguishable, or there is no other way to tell which checkers have made a complete tour, then a player could easily mistake a checker which made a complete tour for one that had not and bring said checker back into the game.