Managing Inventory
You can choose whether to use Endless to manage your inventory or to use another system. You should choose the option that best represents reality. Think of the person that would do a cycle count for your inventory to confirm how much you have in stock. Which system do they use to record that count? That's the system you should choose.
If you choose to manage inventory in another system (such as your 3PL's warehouse management system), you can still make updates in Endless but you should expect that the data will be overwritten at some point.
For each building in your system, you can decide whether to push inventory to other systems or not.