Hi there gsb06,
It's vital that all your information be entered correctly so that all your reporting can be correct. QuickBooks Online is a great tool able to help you create invoices to send to your customers all the while having them entered in your books. I can provide some information regarding customers.
There isn't a way to apply a default location to your customer to help save time with reporting. You can add locations to lines of a transaction in order to help with the reporting, but there isn't a way to have it set by default. Here's an article about how to set up and use location tracking in QuickBooks Online.
I can see how having this be a default option could save you time when creating the invoices for your customers. I recommend leaving feedback in the system by clicking on the Gear icon, then Feedback. The comments made in that section are taken into consideration when designing new features for future updates of QuickBooks Online. I'll pass along your feedback on my end as well.
If you have any other questions, feel free to reach out here.
