(reference: 10-11-99 by Blair)
To expand on reason #2 -- If your opponent has out an active and several
benched which can all take 50 damage, then you are guaranteed a knock-out in
two turns by using Swords Dance; if you don't your opponent can retreat
after Scyther's first attack, so no knock-out.  This is particularly useful
if your opponent has two Dodrio's, each with 10 or 20 damage, so you avoid a
heavy-damage Rage retaliation.
--jrsy