Josh,
This is a cool piece of functionality. If the Customer allows you to combine many Sales Order that have shipped Shipment, onto a single Invoice, then flagging the Customer that Combine Shipments = TRUE. Now you might think this is the same as Get Shipment Lines and it is but the Combine Shipment does this automatically for a Customer without having to pick the Shipment Lines. If you search for Combine Shipments and Option box opens, then...
1. Fill in the fields
2. Choose to Post Invoices.
3. Click OK
If you forget to click Post Invoices, you will need to manually Post the Invoices as they will be created, just not auto posted.
Hope this helps.
Thanks,
Steve