A couple of our customers store inventory items and their current stock levels in Calpendo.  Once a booking has completed these customers allow a user to submit how many of a certain inventory item was used.  If, once the workflow has subtracted that value from the stock level, the resulting stock level goes past a reorder number set for the inventory item it will trigger an email with information regarding the inventory item which needs to be restocked. This could go either to a designated contact for inventory ordering or to a named person responsible for that inventory item.