How To Re-install YOSEMITE If Necessary?

How to re-install YOSEMITE if necessary?YOSEMITE runs like clockwork on your Mac, but no one is immune from a major glitch. I cannot recommend that you perform backups to avoid losing all your data, on the day your hard drive or Mac come to give up the ghost. One is never too careful in this area (see page "Backup and clone”). If you are ever faced with the need to reinstall YOSEMITE or because