The Fire Bomb is a simple but deadly building that is placed and constructed like any other building. However, it is actually an explosive device and deals damage to enemies when it is destroyed.
Fire Bomb has little use in PvP; players will simply avoid it, and used ranged attackers to destroy it if necessary. However, its main advantage in PvE, of being only a temporary source of damage, is often not an issue in the faster-moving portions of scenarios, where it can help take a lot of ground in a short time. It is often neglected by PvE players without access to Mine, and it even offers an advantage over Mine, of being a target that can Tank a small amount of damage. Pro players use it often, as seen in numerous YouTube videos (eg King of the Giants - @ 1:00 and Crusade - @ 4:40)