1. Wastes glassifier charges (this is the biggest one)
2. Deals damage to nurses, friendly turrets, and secret area crystals when you don't want it to
3. Triggers nonstop counterattacks from the secret boss
4. Sometimes finishes off an enemy when you wanted to get a death trigger off of them (eg soul eating spell)
While I'm complaining, also not a fan of losing nurses to automatic enemy explosions, but I guess that can be planned around, unlike the drone which never stops shooting when you dodge.