Cross customer picking allows Any Product (regardless of Customer) to be added to Any Sale Order.
For example, if you have two Customers and each has one Product:
Customer A → Leg of Ham
Customer B → Balloons
Normally, CartonCloud would prevent you from doing the following:
Creating a Sale Order for Customer B and adding a Leg of Ham to it.
However, by turning on Cross Customer Picking you're enabling this functionality.
With Cross Customer Picking, any Product can be added to Any Sale Order.
To enable this go to Organisation Settings (use Search Anything) then change the selection for this option: