Booster buildings are usually decorative, such as a tree or fountain. When placed near other buildings, they will increase their efficiency. Each booster has its own rate. For example, placing a fountain next to a quarry will increase the quarry's production by 6%. Those bonuses will stack with the use of multiple boosters. Plan your town's layout to allow boosters to be placed next to as many of your buildings as possible. One method is to place boosters in the center of a section of land, then place other buildings around it.