Shipment on Invoice Field in Sales & Receivables Setup Table
If you place a check mark in this field, the program will automatically create a posted shipment, in addition to a posted invoice, when you post an invoice.
If you leave the field blank, the program will create only a posted invoice when you post.
What does it mean in simple user-friendly terms? Well, have you ever seen a posted sales shipment for manually posted invoices like:
This sales shipment has been generated automatically, when user went to Sales & Marketing > Order Processing > Invoices, created new invoice for travel expenses, and invoiced it directly from Sales Invoice screen.
If Shipment on Invoice field is unchecked, sales invoice would still be posted, however posted sales invoice would not be generated.
I think you have a typo in the last line:
If Shipment on Invoice field is unchecked, sales invoice would still be posted, however posted sales **shipment** would not be generated.