If you activated the new Inbox Tabs then after a while you find yourself not liking them that much and would like you old priority inbox back, this is what you need to do.
If you want to make a clean install of the new OS X Mavericks or even the older versions of Mac OS X, than I strongly suggest you to create a bootable OS X key or a drive.
If you use a lot of different usernames and passwords it is difficult to remember all of them. KeePass is an interesting solution where all your passwords are kept in one safe place and protected with one password.
