1) They have the Unicorn Bow, or the enemy is within direct firing range (about 6 cells).
2) The enemy's defense is very low (neutrals of levels 1-3, low-level troops of heroes from the Academy, Inferno, or Dungeon).
New Druids are useful for Chaos factions. Enchanting a ballista is difficult, but even without it, 3 enchanted arrows (e.g., with Meteorite), with a spellpower of around 30, will deal considerable damage to the enemy.
Alt-grade and changes to the skill wheel add a large number of tactical options for playing as an Elf, which is a welcome addition.