Here you can choose whether you want to compress or encrypt your archives. You can use either compress(1), gzip(1) or pgp(1).
In the menu for choosing the compression/encryption filter you can also pass any useful command line options to the filter. A rather useful one is the parameter "-1" for gzip(1). A gzip-compressed file with option "-1" is about 10-20% larger than with the standard compression, but compressing it is about twice as fast.
Do not be surprised, compressing a long backup can take quite some time (during which your tape might not operate if you are using double-buffering ).