There seems to have been a lot of confusion around this subject over the last few weeks, much of it caused by seemingly conflicting Periscope broadcasts. Broadcasters often forget to point out (or assume viewers know) which script style the lesson they're giving applies to. As everyone else has said, the answer is "it depends which script you're studying". In general:
- Copperplate (and Engrosser's script in particular) - Finger/wrist movement
- Spencerian - Muscular/arm movement
- Ornamental Penmanship majuscules - Whole arm/Shoulder movement
- Flourishing - Whole arm movement
- Business Penmanship - Muscular movement
Even if you're learning Engrosser's, the muscular and whole arm drills are useful for warming up and encouraging a light hand and freer movement. However, when writing the script your wrist should be planted and finger/wrist movement used, to give the necessary control.