> I make sure I mark the most recent email as read. Then, I look back until I find the next email marked as read.
I don't have to do any of this or have a special system. I just read my email. If an email is unread, it's unread. If it's in the inbox, it hasn't been dealt with yet.
That's where the "need" comes from: it's the simplest way of achieving exactly the same result you achieve with your system.
I use basically the system described above, because I have tons of emails that I never intend to read (e.g., from mailing lists). The system of leaving them all in my inbox is simpler than having to explicitly archive them all.
I don't have to do any of this or have a special system. I just read my email. If an email is unread, it's unread. If it's in the inbox, it hasn't been dealt with yet.
That's where the "need" comes from: it's the simplest way of achieving exactly the same result you achieve with your system.