[SixOfSpades]

When Volothamp's Comeuppance goes so far as to actually suggest that a particular spell would be useful in a certain area, it's because the area has the potential to cause a LOT of head-crashing-into-wall syndrome among newbies. If a party has the Ring of Free Action, the player won't be a newbie anymore, and their Warriors will probably make the Save anyway. Newbies are also not likely to put a Small Shield on a Tank, so the Demons are sure to claim at least 1 or 2 lives. Potions of Invulnerability are also not plentiful until late in the game (and newbies generally don't have the foresight to hoard and use them wisely), and I've never seen Potions of Free Action to carry any benefit whatsoever.

Yes, you can beat the Demons without casting Free Action. But for those who happen to blunder into the Sphere in Chapter 2, one little spell can save so much headache.