Where this matters:
- When backing up 100s or 1,000s of database or text files, this can mean a space savings of 10-30% vs. regular zip files.
- When you're archiving something to CD or DVD and space is still a concern.
- If you want to password-protect a file you're sending.
- A few files you're emailing to a friend. A little extra space here and there isn't going to matter.
- Don't re-compress ZIP files nor JPG or MP3 files. These files are already compressed. PDF files will sometimes compress more, sometimes not.
- When you install, the program will pop up with an annoying notice about downloading the RAR binary but the program will download the files automatically for you. If it asks, select "Install inside rarify". Then start the program and select "Rarify" from the menu.
- In the preferences, turn the compression meter all the way to the right. This is because if you want a speedy, normal compression, you should be using OS X "compress" program instead.
- To compress, just drag a file or files onto the purple-green-and-blue dock icon:
Note that most Macs cannot open RAR files by default. Recipients of your files will need a program like Unarchiver.
Crossover users: I strongly recommend the Windows 7-zip program in OS X. Its .7z format is similar in speed and compression to RAR and has tons more features.