This Exchange TechNet Wiki page explains the Microsoft support lifecycle for the Exchange Server application, Windows Server operating system, Office, and client operating system family products.
Understand microsoft support lifecycle allow you to know when the product is "end of life support" and Microsoft will only provide limited support afterwards. This will prevent " What does it mean my version is no longer supported? "
Common reason WHY upgrade:
Refreshing new appearance, continuous security protection update, better performance, more add-on feature, microsoft supported, user friendly, productive and many more reason you can feel it, when you try it.