What is in this critical update?

This update contains all bugfixes or improvements that are integrated in rollup 12 or higher. It contains an update for the server and outlook client.

And it includes a new feature of CRM 2013. This features moves the CRM client workload into its own process. That means that the CRM client doesn’t share memory anymore with the outlook process.

Who needs this update? And why you just don’t install a higher rollup?

Every server and client running rollups between 6 and 11, that can’t be updated to rollup 12 or higher because of compatibility reasons, such as unsupported JavaScript customizations.

How to install.

For the server it is easy, just run it and done.
Bot for the outlook client you have to uninstall the client and reinstall the Client CU. And Microsoft advises to disable the automatic update for CRM on the client computer.

For more detailed info about al the bugs or issues solved by this update, I refer to the article of Microsoft.