Destination type is driven by various factors- such as, If you are using an Inventory item to create the requisition and populated the destination subinventory while creating the requisition then the destination type will be defaulted ads "Inventory", otherwise all the expense or description based lines are added to the requistion as "Expense".
1. The destination type can be expense or inventory for inventory items. If the item is delivered to an end user then the destination is considered expense destination, but if the item is delivered to an inventory stock location then the destination type is inventory. The deliver to location defaulted or chosen during check determines whether the item is delivered to inventory or expense destination. Choose a different deliver to location to see the differences.
If the item is inventory then the destination type will always be used as inventory
If the item is expense then the destination type can used either expense or inventory
Also review the below notes,
Where Is The "Deliver-To Location" In Iprocurement Preferences Defaulted From ? (Doc ID 1088823.1)
How To Setup Default Deliver-To Location For Expense Item On iProcurement Requisition (Doc ID 946224.1)
How / Why Does the Deliver-to Location Map to an Inventory Org ? (Doc ID 1549338.1)