Apply security related updates to all software as soon as possible
All software has a life cycle, which also include patches to quickly fix bugs and security loopholes between the major upgrades. The most efficient installation possible of these patches on all the relevant machines is of paramount importance for maintaining the security level.
When a new 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 opportunity for potential exploitation.