Kind of redundant. Both .zip and .rar store an index of files within the archive and are a bit 'inside-out' when it comes what we get from tar.gz.

That is, ZIP is pretty close to what you'd get if you first gzipped all your files and then put them into a .tar.

RAR does a little more (if I remember correctly), such as generating a dictionary of common redundancies between files and then uses that knowledge to compress the files individually, but better. Something akin to a .tar file is still the result though.