Currently Tryton has a default warehouse if there’s only one set.
For a company having multiple warehouses, you’ll have to select the correct warehouse each time this information is needed (sale, purchase, product quantities, …) and most of the time there’s a warehouse you select more than the others (depending of some criteria).
Example: a company could have warehouses in multiple countries. Company users of a specified country will often, by default, use the warehouse of their country.
The idea would be to define a generic method that deliver the default warehouse.
First proposal would be to return a default warehouse set on the user.
This method could be customized and extended to different cases: per company, per employee, per shipping address, per customer/supplier,…