Unlike the others, it's an actual magnetic tape with a slightly rough coating. Recorded on the tape is a message that appears on your screen. If you can read the message, the heads are clean. Slow speed isn't good enough. But the slow speed is even better than the fast speed for some functions.
Special effects are nearly always better at the slow speed.
And you get rewind and fast-forward times that are three times as fast per minute of video. I'd use the fast speed only for baby's first haircut and things like that. Otherwise, slow is the way to go.