Do I need to upload the purchase orders csv file? Where does this come into StockTrim?

The Purchase Order history import is optional. Purchase orders are used for two purposes: 1) to set the on-order amounts and 2) to calculate the lead time. 

However, it's generally easier to set the on-order amounts via the Products csv file instead, so you'd only require this if it's easier to export the purchase orders as a separate file from your IMS. You can also set your lead times within StockTrim at the supplier or product level, or a default system level value. 

In summary, it's good for automatically setting the lead time, or setting the on-order amounts if they are not able to be included in your products csv import. Items that have no arrived date in the PO file will come through to StockTrim as 'On Order'