There are different categories of updates. Different update methods are preferred for different update categories. That said, a certain update mechanism may be the most efficient in a certain update scenario but can very well still be used in another. The different update categories are:
Major updates (that is, full version updates): This update category is typically a major product version update. For example, Microsoft Office 2007 was updated to Microsoft Office 2010.
Minor updates (typically point releases or service packs): This category typically features updates and bug fixes within a specific full version. For example, updating from Adobe Acrobat Reader 8.0 to 8.1. Both are within the full version of 8.
Patching and hotfixes: These updates are typically smaller in size than minor updates/point releases but are essentially within the same update category.
Configuration changes: Configuration changes are typically a very small number of changes. These...