This feature allows to optimize size of archives or compression time.

There are several compression levels available:
1) No compression - recommended for backup multimedia files (*.mp3, *.mpeg, *.dat, etc) and compressed images (*.jpg, *.gif, *.png, etc)
2) Normal - best balance between archive size and compression time.
3) Fast - minimum compression time. Recommended for quick backup, especially on slow computers.
4) Maximum - using to make smallest archives. Need more time than normal compression.

Note: Fast and maximum compression level support only in Pro and Std editions.