Spells in B/X tend to be pretty simple, but even simple spell descriptions can imply some interesting things about how a spell might work in play, including unconventional uses. In the next several posts, I'm going to be analyzing the spells of B/X, at least up to level 3, for both clerics and magic-users.
1. Cure Light Wounds*: This spell is the foundation of magical healing in D&D. It's often claimed that, because it's exclusive to the cleric class, it virtually necessitates that every adventuring party have at least one cleric in its ranks. In B/X, however, a first-level cleric receives no spells at all, so I'm highly skeptical that magical healing was ever meant to be an absolute necessity. A beginning party must make due without it, unless they find healing potions, and unless the party has multiple clerics, they're severely limited in the amount of healing they have at their disposal. At 3rd level, a cleric can cast a maximum of two healing spells per day, and doesn't get any more until she gains access to the 4th-level Cure Serious Wounds spell. (Bizarrely, the cleric spell tables in the Cook Expert rules jump from 2/2 at 5th level to 2/2/1/1 at 6th - gaining access to 3rd and 4th level spells at once! Mentzer Expert more sensibly has 3rd level spells at 6th level, and 4th at level 8. But I digress.) A B/X cleric just can't provide enough healing for a typical adventuring party to get torn up in a fight every couple turns. (This is yet another strong hint that the game is meant to be primarily about exploration, wit, and guile, and that combat is to be avoided whenever possible.)
The reverse of the spell, Cause Light Wounds, inflicts the same amount of damage that the normal spell cures, 1d6+1 points. There is literally no reason why a cleric would ever use this in combat, because it does scarcely more damage than a mace or hammer, and it still requires a normal attack roll. I suppose it might be used for some sort of dark ceremonial purposes, but in battle, it's utterly useless.
2. Detect Evil: At first glance, this spell seems like a total spoiler for adventures with a strong investigation or social conflict element. A careful reading of the description shows that the spell doesn't detect inherent evil in creatures, but evil intent. A goblin or bandit, or the king's scheming vizier, only registers as "evil" if they're actively contemplating an evil act at the time. The definition of "evil" is left to the DM's discretion. It also detects "evilly enchanted objects," though again this isn't really defined. It doesn't say, for instance, whether curses are evil. It's possible to interpret a cursed item as merely defective rather than malicious, so I suppose leaving each individual case to the DM's judgment makes sense, though it would have been nice to have some of these cases stated more explicitly. Also of note is that the spell has a range of 120' and lasts for 6 turns - that's one full hour of in-game time - which means it can potentially remain active for a good bit of exploration. It makes all "evil" targets glow, which would tip off anyone in the area that a spell has been cast, including the creatures detected by it.
3. Detect Magic: Not a lot needs to be said about this one. Like Detect Evil, it causes targets detected by it to glow; thus that information is available to anyone with eyes to see it, not just the caster. With a range of 60' and duration of 2 turns, a sizeable area can be scanned, and it might prove useful to cast it before a major confrontation in order to know which opponents are bearing enchanted equipment or magical enhancements of some sort. Of course, clever opponents might deduce that the party's own equipment that glows is magical too...
4. Light: Just about every gamer knows the combat use of the light spell, casting it at an opponent's eyes to blind it. A saving throw is allowed, but anything that saves as a 9th level fighter or worse is more likely than not to be taken right out of the fight in one fell swoop. It's almost a shame that light is such a potent attack spell, because its more utilitarian purpose is highly underrated. The duration of 12 turns is respectable, though not as much as a torch or lantern, but there are situations when hand-held burning lights are impractical. Some examples include underwater or in very damp places, climbing and other activities for which both hands are needed, in places with lots of combustible materials, and in fights with intelligent subterranean creatures (a lantern has to be an attractive target for goblins, who can see just fine without it and would gain a huge advantage by snuffing the party's light source.) It can be cast on an item, so just stick it to your helmet, and you're good for two hours. This usefulness depends a lot on the DM applying the drawbacks of conventional light sources rather than handwaving them, though.
The reversed spell, Darkness, can be used offensively in a similar fashion to Light. It also might be useful to conceal things. A patch of darkness in a dungeon is a lot less conspicuous than, say, a pile of loot or a stash of rations. A cleric might cast Darkness across the doorless entrance to a room where the party wishes to rest, thus screening them and their light sources from eyes looking at the doorway from the other side. Darkness doesn't foil infravision, though.