Builder's Guild allows me to transform farmhouses, cottages and spires into "toadstool" version. Normally these buildings only drop coins. Once transformed, they start dropping toadstool crafting materials, so the more fungal buildings I have, the faster I can make them. But do they ever produce anything else, useful in other quests/crafting/etc? I do not particularly care for the "toadstool look", so if that's all there is to it, I will ignore it.