Dave prefers we play the tunes slow until we get proficient with timing. As you know, most bluegrass is rather fast, >100 BPM, but few of us could play that fast and maintain good timing (speaking for myself anyway) I set my met for a 1/4 note 55 BPM, to learn the rhythm chord progression. When i can make the chords accurately, i'll add 10 BPM, and so on. After a while, good timing becomes somewhat learned. In my humble novice opinion, speed without timing is just noise. I'm still learning this, thats why you see Dave and other good guitarists tap their foot to keep that rhythm.