The option defines the level of compression applied to the data being backed up. The available levels are: None, Normal, High, Maximum.
The preset is: Normal.
A higher compression level means that the backup process takes longer, but the resulting backup occupies less space. Currently, the High and Maximum levels work similarly.
The optimal data compression level depends on the type of data being backed up. For example, even maximum compression will not significantly reduce the backup size if the backup contains essentially compressed files, such as .jpg, .pdf or .mp3. However, formats such as .doc or .xls will be compressed well.