Case study (EE14 on odoo.sh, Multi-Company):
Company A needs an item that is not in stock in its own warehouse. The purchaser should now have the possibility to check in the warehouses of the parent company as well as in the warehouses of the other subsidiaries if the item might be in stock there and then order it there.
Is there any way to implement this without each purchaser in all companies having the ability to access multiple companies? That would probably be complicated again, because the buyer would have to have different rights in his own organization than in the others.