How strictly do you define need? I've been living as an adult long enough that there have been countless times I've searched for photos and emails from one or two decades ago. I distinctly remember the first time I met an Inbox Zero person. It was so important to her to militantly delete everything she had dealt with, and to me, the disadvantages from that practice far outweigh the advantages.

Inbox Zero just means to deal with messages as they come in, then move them out of the inbox, generally to an archive section.

If she was hard-deleting everything, she wasn't just Inbox Zero, she was F---s Zero, too.