Surface-mounted, the door slides along the wall on a visible track or one hidden behind a fascia. It fits on a finished site, doesn't touch the partition, and costs considerably less. In exchange, the stretch of wall it parks against can no longer take furniture, a switch or a picture.
Pocket sliding, the door disappears entirely into the thickness of the partition. It is the more elegant solution and the only one that consumes no wall — but the cassette must be installed while the partition is being built. On a site already boarded out, it is no longer a reasonable option.
If you are building or doing a heavy renovation, decide now: it is the only moment when a pocket door costs almost nothing extra.