Tommy Emmanuel CGP uses a capo, usually a Kyser - nobody can argue with that! Indeed, it was when I first saw him using one many years ago playing in Australia that I decided to get one, and I've never looked back.
My favourite arrangment is to use a Shub capo to bar across all six strings anywhere on the fretboard, and then use a Kyser in reverse position barring all but the sixth string.
This gives the equivalent of a 'drop D' style tuning anywhere on the neck.
It gives the advantage of a deeper bass note to play on the sixth string (eg. the 5th note in a G shape chord or the 1st note in a D shape chord). But it still allows you to play say a full six string chord strum as, unlike with a true drop D tuning where the bass string is actually detuned, the sixth string plays the 'correct' note when held down eg. when playing a full G chord shape or a C chord shape with the sixth string held down playing the 5th note of the chord.