how to determain those no longer required packages

[Muayyad AlSadi]

warning: leaves in package-cleanup or remove-with-leaves could be your
preferred application because it's a leaf [ie. no installed package
depends on it, eg. pidgin or uget]

there is a flag in conf of remove-with-leaves to exclude non-library
binary packages from being removed

Yum does not trace if some package is installed per user request or
pulled for dependency