Associating a purchase order to a visit does affect the job costing inside SingleOps, and it will appear in the Expenses table on the job's page once the purchase order has been approved.
Associating a purchase order to a job does not affect the job costing inside SingleOps. It will, instead, appear on the Purchase Order table on the jobs page.
It is worth noting that the two appear the same from the QuickBook's perspective after they've synced. It is only within SingleOps that they differ.
Why isn't the Purchase Order Appearing on a Job or Visit?
If you find that after adding an expense to a purchase order, it still doesn't appear on the jobs page... here may be why:
After the expense has been added to the visit by adding it inside a new purchase order, you must also approve the purchase order for it to show in the expenses table on the jobs page.