Apple routinely releases updates for macOS and OS X that are available through either the Software Update process or the Mac App Store, depending on which version of macOS or OS X you're running. These software updates typically offer the easiest method of ensuring that your Mac's operating system stays up to date. However, you might still encounter a problem.

If your Mac freezes, loses power, or otherwise prevents an update from completing, you’re left with a corrupt system update. This can manifest as simple instability with intermittent crashes or system or application freezes. In the worst case, you may experience boot issues, forcing you to consider reinstalling your operating system.

Another issue is related to Apple's incremental approach to updates. Because Software Update only downloads and installs system files that need to be updated, some files may be out of date relative to other system files. This can result in intermittent system or application freezes, or the inability of an application to launch.

A software update problem is not a common occurrence, and most Mac users never see it. However, if you’re having unexplained problems with your Mac, a faulty software update could be the culprit. Ruling out the possibility is easily done with a combo update, which is a regular update on steroids.