Assumes you'll be reading from one end to the other - "Tape ARchive". (The age of the command shows...)
Does not do compression, but you can compress the entire resulting stream by piping it through e.g. gzip and bzip2 (done internally with -z or -j)
Stores unix file attributes: uid, gid, permissions (most notably executable). The default may depend on your distribution, and can be toggled with option