By default, the Location field is not required for invoices in Netsuite. MineralTree likewise does not require the field when entering bills, or posting them to Netsuite.
However, you may find that some invoices will not post to Netsuite without Location defined, via an error like this one:
This occurs when the invoice is linked to a Purchase Order that itself has a Location value. In these cases, you must set Location at summary and/or line level on the invoice in MineralTree. You will then be able to post to Netsuite.