AFAIK it doesn't do anything with the rpm database, it only removes packages, headers, metadata and cleans out the sqlite database that yum uses. Have a look at the man page for yum for more detailed information. That for the yum part. If you want to 'clean up' your rpm database to make sure no 'old' references might be hanging around you can follow the following procedure:
- Move the existing database files /var/lib/rpm/_db* to another location for backup
- run the command:
But under normal circumstances the rpm database occupies very little space and unless your having issues with the rpm related commands and assume a database corruption, there is no need at all to perform the above actions. After all 125 Mb is not large at all nowadays.