They are suppose to be fixes to existing problems. There is always a README and the installation script will not function unless the README is included in the downloaded files.
Unfortunately, VERITAS sometimes places new functionalities or changes in processes in the MP's. That is bad because that sometimes introduces new problems without warnings.
It is not absolutely necessary to install MP's unless of course there is a fix to a problem in your environment. Carefull reading of the README is greatly encouraged because sometimes work arounds are suggested in place of installing the MP.
I would also be careful not to get too far behind in the MP's and even the NetBackup versions. On the other hand there is a potential of lost sleep if you too eagerly install MP's when they first come out. I usually run an MP or two behind the bleeding edge.
Again, the trick is the README file. It is long but does have good information.
Bob Stump
Incorrigible punster -- Do not incorrige