Here are descriptions of a few useful Yum plugins:

The presto plugin adds support to Yum for downloading delta RPM packages, during updates, from repositories which have presto metadata enabled. Delta RPMs contain only the differences between the version of the package installed on the client requesting the RPM package and the updated version in the repository. Downloading a delta RPM is much quicker than downloading the entire updated package, and can speed up updates considerably. Once the delta RPMs are downloaded, they must be rebuilt (the difference applied to the currently-installed package to create the full updated package) on the installing machine, which takes CPU time. Using delta RPMs is therefore a tradeoff between time-to-download, which depends on the network connection, and time-to-rebuild, which is CPU-bound. Using the presto plugin is recommended for fast machines and systems with slower network connections, while slower machines on very fast connections may benefit more from downloading normal RPM packages, i.e. by disabling presto. The presto plugin is enabled by default.

The protect-packages plugin prevents the yum package and all packages it depends on from being purposefully or accidentally removed. This simple scheme prevents many of the most important packages necessary for your system to run from being removed. In addition, you can list more packages, one per line, in the /etc/sysconfig/protected-packages file^[1] (which you should create if it does not exist), and protect-packages will extend protection-from-removal to those packages as well. To temporarily override package protection, use the --override-protection option with an applicable yum command.

The rhnplugin for Yum provides support for connecting to Red Hat Network (RHN). Systems registered with RHN are able to update and install packages from Red Hat Network.

Refer to man rhnplugin for more information.

This plugin updates metadata for PackageKit whenever yum is run. The refresh-packagekit plugin is installed by default.

Discovering information about and applying security updates easily and often is important to all system administrators. For this reason Yum provides the security plugin, which extends yum with a set of highly-useful security-related commands, subcommands and options.

You can check for all security-related updates as follows:

~]# yum check-update --security
Loaded plugins: presto, refresh-packagekit, security
Limiting package lists to security relevant ones
Needed 3 of 7 packages, for security
elinks.x86_64                   0.12-0.13.el6               rhel
kernel.x86_64                   2.6.30.8-64.el6             rhel
kernel-headers.x86_64           2.6.30.8-64.el6             rhel

You can then use either yum update --security or yum update-minimal --security to update those packages which are affected by security advisories. Both of these commands update all packages on the system for which a security advisiory has been issued. yum update-minimal --security updates them to the latest packages which were released as part of a security advisory, while yum update --security will update all packages affected by a security advisory to the latest version of that package available.

In other words, if:

...then yum update-minimal --security will update you to kernel-2.6.30.8-32, and yum update --security will update you to kernel-2.6.30.8-64. Conservative system administrators may want to use update-minimal to reduce the risk incurred by updating packages as much as possible.

Refer to man yum-security for usage details and further explanation of the enhancements the security plugin adds to yum.