I like, and try, to keep a clean system.

I know I can use yum to list my installed packages. Is there an easy, fast method for cleaning up packages that are irrelevant, such as extra packages that I don't use, and that are not requirements for other packages?

As an example, I don't know what yelp is, so I know I don't directly use it.

Utimately, only _you_ know what you don't use. Look at manpages to determine program functions. The RPMOrphan application can sort packages by incremental access times to identify probable candidates.

# rpmorphan --all --access-time 15

That will list the orphaned packages unused since 15 days or more.

Thanks for that info. Is 'orphan' the term used for packages that are dependencies for others that have been removed?

Yes, "orphan" means that no other package depends on it. For example, suppose that you installed the xyz application, which in turns requires the abc package. If you uninstalled xyz just by itself, then the abc package would still remain on your system, but nothing would be using it, so it's just taking up space, and similarly it could be safely deleted.

However, as far as your original question, as already mentioned, what is considered 'irrelevant' or 'unused' would vary from one person to another, and there are no hard and fast rules. As a very general comment though, if your distro has installed a particular package, there's a reason for it. Personally, I would be very hesitant about arbitrarily removing packages simply on the basis of not recognizing their names, and I would warn that if you plan to move forward there is a chance you could negatively impact your system. Keeping a clean system is an excellent idea, but I would recommend that you research each package's purpose/function before getting rid of it...

I most definately agree with you on this. I was just hoping that there was an easy way to determine which packages were orphaned and unused, and could safely be removed.

For instance, when I yum installed one application, it did install about 5 dependencies, of which I don't have a list. I removed the application, but I know that did not remove the dependencies.

Another, related question:
When a package is removed, are conf files removed also?

Generally, the config files in the /etc directory are not removed.

Out of curiosity, if the program isn't taking space and isn't being used, why remove it? You may need it later and not have access to reinstall it. Just a thought, I figure space is cheap, why worry?

Clutter. That's like asking why you would get rid of your kid's toys when they've long stopped playing with them.

For info, debian keeps track of which package is installed as a dependency and which ones were explicitly installed.
So it will remove dependency packages for which no manually-installed package depends.

On my system, everything is automatically removed.

This ONLY works if you only play with packages. If you have installed from source, then this automatic mechanism will break things.
The solution is to always create a package from a source you want to install.
On Fedora you have to do it because less binaries are packed.

And that's why the default is to leave them behind. You can easily command rpm to output those file before you remove the package and then delete them yourself if this is a concern. Or you can option rpm during reinstallation to write over those same files if you prefer the native configuration. It's completely up to the user, but there is no harm in leaving the previously touched configs around...just handle it however you wish.