[CentOS] necessary/unused rpm packages

Is there a way to identify if an rpm package is unused, or how much it is
used?

I would like to reduce my load time by removing unused packages in my
kickstart, but do not want to cause problems for users on active systems by
guessing which ones are not necessary (I load everything with kickstart
now).  If I could find the packages are not used I could start by excluding
them from a load and be fairly certain my users would not be impacted.
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