By default, Virtualmin runs the `gzip` or `bzip2` commands for compressing backups with no additional parameters. This means that the default compression level and format will be used. However, you can use this field to enter additional parameters, such as `--fast` to make your backups run faster (at the cost of requiring more space), `--best` to get better compression (at the cost of CPU time), or `--rsyncable` to make the file more easily replicatable.