I am forever reminding people to make sure they have backups because if you don't, there will come a day you will need one. I back up using SuperDuper and it's a great piece of software particularly for drive backups, but another which is equally of value is Apple's TimeMachine.
I noticed the other day that instead of having a whole bunch of Notes in my Mail application, I only had about 10. Knowing I had many more, I needed to figure out an easy way to find the 'lost' notes and to bring them back into Notes so I could access the information in them. I fired up TM[that's TimeMachine for short] and went back into April and found all the missing notes and restored them, so I could review and edit or delete them as appropriate.