Sorry, Caveat?

If I'm reading right, please correct me...

If I press yes to this pop up, it will delete/compact/disable ALL the
messages that are in my Inbox and my Sent Items box...
As Well As...completely deleting the deleted messages that I'd thought
I'd Emptied from the Deleted Items box.

I'm sure I've pressed OK before and I lost a LOT of information from
the Sent Items folder.
I use this folder all the time as my brain is a sieve.
Am I right - should I transfer them all to a different personally named
folder before pressing yes?

Thank you.
From...
Old person who doesn't really understand computers but is darn grateful
for help