Why should I upgrade from Windows 7 to 10?

Microsoft is pushing its free upgrade at Windows 7 users and Tom wonders what the benefits are. The answer includes opt-out information for refuseniks

You haven't answered the most obvious question of all: why should I upgrade from Windows 7 to 10? What are the benefits? Please give a straight answer, which can include technical stuff. Tom

In the long term, I don't think the question is "Why?", it's "When?" Eight months after launch, Windows 10 is running on 270m devices and it's not going away. Some large organisations have already started to move, one of the most notable being the US Defense Department, which has started installing Windows 10 on 4m PCs.