Even if your Mac has a huge hard drive and you have the speediest possible access to the Internet, you need compression software.
Compression software uses a special algorithm to make files smaller. In addition to the obvious advantages of using hard-drive space more efficiently, a compressed file can shave a hefty percentage of time off moving files to or from the Internet.
It wasn't so many years ago that you had to think long and hard about which compression method you wanted for your Mac. The sixth edition of The Macintosh Bible, published in 1996 (an eternity ago in computer time of course), listed four product families in this category, and even then it didn't mention them all (it excluded a fairly popular entry, DiskDoubler ...