Minecraft wiki entry for Things_not_to_do, associated text: Lava is a dangerous resource. The player should not keep lava in their hotbar unless they are about to use it. Death can result from accidental use of a lava bucket, as well as damage any builds in the immediate area. Apart from lava, having items in the hotbar which are either not essentials (like weapons or food) or in use consumes valuable space. Unless the player is going to throw them or has nowhere else in their inventory for the items to go, leaving these items there just clutters up the hotbar, setting the player up to waste time later.