Though Fungal Dwarves are not happy to spread out typically nor really want reach most of the time, Stimshrooms provide an undeniable threat in their deck. The opponent must be ever mindful that a Stimshroom-empowered unit does not have reach to where they were not expecting. 
You don’t need much from this event to be worth it. If thanks to Stimshrooms your Fungal Beast can reach a target that will become a Spore Carrier, often that is all that is needed to justify playing this card.