For example if your training hall is level 3, your heroes can only be level 7 maximum. Imagine you were playing all alone, or in a 1-person guild you created just for yourself then the level of your gatherers, crafters, heroes, and other things would be limited by the level of their respective buildings.
The guild is an interesting concept in Shop Titans, because you are far better off if you join one, but it doesn't require you to do much.
