Apply security related updates to all software as soon as possible
All software has a life cycle, including patches for bugs and security loopholes between the major upgrades. The most efficient installation possible of these patches on all relevant machines is an important for maintaining the security level.
When a patch is released, it is rapidly studied by ill-intentioned users, who try to identify the security loopholes that the patch closes. Applying the patch as soon as possible reduces the window of attack for potential exploitation.