This happens a lot... Someone decides to go on a quest, and sends a sending to everyone in Sanctuary asking for adventurers to come and join him. Several people come to his aid, and they immediately leave to perform the task.
This is not how a decent party should operate.
One of the things that annoys me the most in Escape from the Underdark is that most of the time, the party doesn't plan its spell tactics. Some are just too impatient to wait for the prepared spellcasters to prepare their spells, while others feel that it is metagaming to choose which spells to prepare based on the composition of the party.
Magic is everywhere in Toril. Unless you are a member of a reclusive race which is ignorant of magic, you will not be completely ignorant of how magic works. Yes, even if you have no ranks in Spellcraft.
The typical Torilian knows that there are different ways of using magic. He knows that some draw their power from nature, some from dieties, and some from the world itself. He knows that clerics and druids can heal, and that wizards and sorcerers can turn him into a toad.
He does not how Cure Light Wounds works, but he knows exactly what it can do. He does not know how Fireball works, but he knows that it is an effective siege weapon.
And if he is a member of an adventuring party which contains a spellcaster, he probably knows the names of some of the spellcaster's spells, and what they can do.
For example, in Keith Baker's novel, The Dreaming Dark Book 1: City of Towers, Daine, a fighter, orders Saerath, a wizard, to bring down an stormship once it gets in range. When it does get in range, Saerath then casts Dispel Magic ("EMP") at it, temporarily disrupting its elemental ring ("engine"). The stormship crashes before its elemental ring gets back online.
Daine has no idea how Dispel Magic works. He does know what it can do and what it can't do. He knows that it can disrupt magic, but he also knows that it has a maximum range.
How did he know this? Obviously, Saerath told him behind the scenes. It is important for Captain Daine to know what his subordinates can or can't do.
The three main prepared spellcasters are the most powerful classes in the game. This is because they have access to a very wide variety of spells.
However, their main drawback is that they have to prepare their spells in advance. They have to know ahead of time what spells to prepare, where to cast them, and when to cast them.
I prepare spells based on the composition of the party. Three melee combatants? I prepare three Magic Weapons (or three Greater Magic Weapons) and three Flame Weapons, and I tell the other spellcasters not to prepare these spells anymore. If the quest requires stealth, I prepare Invisibility. If there are too few melee combatants in the party, I prepare summoning spells.
Coordinating your prepared spells with the needs of your party is not metagaming. It is in-character, and it increases the party's chances of survival.
What do you think?