Not at all... some areas would contain harder monsters while others areas would contain easier monsters, so the player has to be smart about not going into an area that has monsters that are too powerful. Then when the player gets to a higher level he/she would be able to enter areas with higher level monsters without being killed. This adds replayability to a game because the player is always trying to get strong enough to be able to survive a harder area, perhaps one that contains the items needed to kill monsters in an even harder area, which is needed to level up to the strength needed to get to an even harder area.
