As a primarily Windows developer, perhaps I'm missing something cultural in the Linux community, but it has always confused me.
When downloading something that the files are first put into a .tar archive then zipped. Why the two-step process? Doesn't zipping achieve the file grouping? Is there some other benefit that I'm not aware of?
gzip and bzip2 is simply a compressor, not an archiver-software. Hence, the combination. You need the tar-software to bundle all the files.
ZIP itself, and RAR aswell are a combination of the two processes.
In my Altos-XENIX days (1982) we started using tar (tape archiver) to extract files from 5 1/4 floppies or streaming tape as well as copy to these media. It's functionality is very similar to the BACKUP.EXE and RESTORE.EXE commands in DOS 5.0 and 6.22 as supplements, allowing you to span multiple media if it couldn't fit in only one. The drawback was that if one of the multiple media had problems, the whole thing was worthless. tar and dd originate from UNIX SYstem III and has remained a standard release utility with UNIX-like OS' probably for backward compatibility reasons.