Use case example - I just went out to a break-fix customer's business to blow the dust out of all their computers and do some other maintenance. I touched 7 computers. Should I make 7 tickets? I definitely only want to send the customer one invoice. So then, if I want to put all that on one invoice, I would have to mark all or all but one of those tickets as non-billable, but they are billable.. Another example, I set up a new laptop for a community customer, and then transfer the user's data from the old laptop to the new laptop. There are two assets involved, but in my mind, this should also just be one ticket.
An alternative option that I think would achieve a similar result; the ability to create an invoice within a project that becomes associated with all tickets in that project. I could create a project, put all 7 of those tickets in the project, and then generate one invoice from the whole thing, as it was all one job done at once.