We've found there ideally should be multiple invoice templates available - especially paid vs unpaid invoices. Sometimes customers, especially business customers, may ask to be emailed an invoice for their records after they've paid in store, and then being hit by a 'Pay with PayPal!' button may make them complain. As well, with recurring invoices we know they're going to pay and we know how they'll pay, so we don't want to risk them going from a 0-cost bank transfer to costing us 2.7% in paypal fees because we invite them to. We do want to invite unpaid invoices to pay with paypal though.

This isn't limited to the paypal thing, but because we want to keep the wording in line with the context we usually just save pdfs and email them manually. Which isn't ideal, but it's a budget way of doing things. Having multiple templates would mean not having to go through each of our recurring customer each month and emailing them ourselves.