From LQWiki

why would you use tar to copy files?

cp -r is broken on older systems - using tar is thus portable. Dysprosia 19:14, Aug 30, 2004 (EDT)

Is it only possible to extract all files, or can single files be extracted?

I don't know how good the Linux man pages are, but man tar on my 'BSD machine says: "-x Extract files from archive. If any files are named on the command line, only those files will be extracted from the archive." Dysprosia 07:34, May 11, 2005 (EDT)