We use tickets as a foundation for communication with our clients. As such, a quote and invoice is part of my ticketing process. Emails sent to customers regarding a ticket's quote and subsequent invoice should fall under the ticket's communications as well as the billing contact if that is selected.
Right now to send a quote for a ticket I need to click on the client from the breadcrumbs, click on quotes, find the correct quote, click the three dots and click guest URL, in the new window (that now shows someone viewing the quote) I copy the URL from the address bar and go back to the ticket, type in something like quote #123 and hyperlink it with the copied URL. Crazy workflow I know, but its better then merging 3 tickets for every ticket that has a quote and invoice as I quite literally need to pay a human to do this and want to instead pay you to automate my problems away.