3rd edition tricks: Memorizing spells

So one aspect of spell memorization that is rarely used is the fact that you don't actually need to fill all your slots at the beginning of the day. After a rest (or after a specific prayer time) you generally memorize your spells and pick a specific spell for each spell slot. But you don't have to. At any time, you can spend 15 minutes and memorize a spell for an unused slot. This applies to both Arcane and Divine spell casters.

So how is this useful? An empty slot is useless in battle. But many spells you might cast are non-combat spells. For example, you might leave a slot open for a knock or comprehend languages spell out of combat. If you did not need to use these spells and were running low, you might instead put a combat spell in the slot. Rope trick is a great spell for camping, but you never need to memorize that spell until you start camping, so it is always better to leave that slot open just in case you need another spell.

Changing your spells mid adventure can also be used to respond to things. Maybe you discover that you are going to be fighting undead in some crypt. Death ward can make a huge difference.