scp is miserably slow on transferring lots of small files and this can be wildly faster, plus you get your choice of compression program based on what is on each side of the connection and what the bandwidth vs. CPU is.
In the early days of Unix (before rcp was a given), tar pipelines were a common way of moving ) from one machine to another on the network. It was a little nicer than FTP, not only because it didn't need an admin to set up the FT server, but also because you could transfer the files to any directory that you could cd to and had write access to. (And of course, tar made it easy to send a bunch of files and directories at once, too...)
scp is miserably slow on transferring lots of small files and this can be wildly faster, plus you get your choice of compression program based on what is on each side of the connection and what the bandwidth vs. CPU is.