I use Spark email client connected to various Gmail accounts for my email and I follow some rules when dealing with email. I heavily use labels for indexing important emails and approach emails in GTD way, actioning on every email and keeping my Inbox as close to 0 as possible.
I subscribe to a few newsletters and unsubscribe from anything that brings no value and only adds noise.
Gmail doesn't have folders. All your messages are saved in All Mail. Everything else (Inbox, Starred, Drafts, user-labels, etc) are just "views" into a subset of the messages in All Mail. And since there's only one copy of any message, if you delete it from any label, you're deleting the only copy, so it's gone from all of them. If you delete a label you remove that "view", but the messages are still in All Mail.