If you want to use a single warehouse for multiple companies, you need to be able to transfer all the inbound/outbound documents from these companies - it could just be intercompany within one Operations instance, or a company using a different ERP system altogether. For this purpose, sales and purchase orders may be overkill, since they are rather "heavy", and more importantly, have financial impact which is not needed in this case.

To address this use case, I propose a pair of inbound/outbound documents ("warehouse input"/"warehouse output"?) that would be enabled for all warehouse functions, but would not have any customer/vendor (maybe just a link to a global address book or even just an address directly) and no financial impact at posting or on the stock itself.