I've worked with Windows for the majority of my adult life.  I can only count a few times where a Windows update has created an issue.  One of those was on a Windows 2000 Server running an APC daemon for power management.  I've managed upwards of 50 computers at a time and remotely deployed updates, scheduled them to automatically install, etc.  Sometimes an update changes the way something looks.  Almost all updates are for security purposes.  Protecting you from some new website hack or preventing someone from installing something on your PC via a web link.  Yes, the majority of updates and patches they send out are patching something that is very remote or theoretical but they wouldn't do it if there wasn't a real risk.

PLEASE PLEASE PLEASE keep your PC (and other devices) up to date unless you have some very real reason for DELAYING the install.


Also, don't click on update links in your email.  Initiate the updates from the Windows Security Center or from a specific app.