Suppose you have two artifacts: Flaming Hellsword of Death, and Mithril Plated Boots of Speed.
You want both to be useable by a berzerk, and only a berzerk. You want the berzerk to able to hold both artifacts and switch between them whenever he wants (using the artifact inventory feature). Therefore, we set each artifact to have a monster restriction of "berzerk".
Now, the purpose of the Boots is to make unit move faster, and to achieve that effect, we need to override the owner's monster tag (e.g. berzerk.mons becomes berserk_fast.mons).
Now the question is, if the berzerk picks up the boots first and "uses" them (thereby overriding his monster tag) will he be able to pick up the sword (which has a monster restriction of "berzerk")? Or, will we have to unequip the boots to pick up the sword?