Many emails nowadays are about order- and reservation-confirmations (e.g. restaurants) or venue-tickets (e.g. concerts, theatre, etc.).
We need them until a certain date or time to prove reservation or payment and become worthless after that specific date. At the venue, my attention is not at deleting the now obsolete email that will clutter my mailbox for another 6-12 months until a “spring-cleaning” of my mailbox.
I’m currently doing a cleaning-session: easily 40-50% of my emails could have been deleted automatically after a specific date I could have chosen right when I received the mail and created an event in my calendar.