This option in the command line tools, limits the amount of changelog information that is included in the repo metadata. This in turns has a dramatic effect on the amount of actual on-disk storage yum uses on the client nodes (xml and sql). Currently without this option on-disk caches can exceed 6+ GB. For comparison, the same cache against an identical repo, but with manually generated metadata was around 54MB.
This is currently preventing us from more widely adopting Artifactory as a yum repo provider within our infrastructure.