Specifying How Yum Downloads Updates

[Bruno Wolff III]

On Wed, Apr 15, 2009 at 07:25:45 -0500,
  Bob Gustafson <bobgus at rcn.com> wrote:
> 
> Similar situations occur when dealing with libraries: generally these get
> installed since packages containing applications depend on them. When the
> application-package is purged, the library-package might stay on the system. Or:
> when the application-package no longer depends upon e.g. libdb4.2, but upon
> libdb4.3, the libdb4.2 package might stay when the application-package is upgraded.

And unless you are short on space that isn't particularly a problem.
There are tools that help find leaf packages if you want to do some pruning.
I am pretty sure that there is even something that will notice that a
package getting removed will make something a leaf and remove that too.
I don't use it, since I typically like kitchen sink installations, so I
don't have exact details for you. It shouldn't be too hard to find though.