There are some players who like to treat their favourite spell as the all-purpose answer to everything. It's usually something destructive, like Fireball.
Orcs are attacking? Cast Fireball!
The evil knight is kidnapping the princess? Fireball!
We need a way to cross the river? Fireball!
So when players start coming up with reasons why their favourite spell might not be perfect for some occasion, best not to argue.
GM: Unfortunately, the droid army has beaten you to the city.
Obi-Wan: From the other side of the planet?
Qui-Gon: They probably took a shortcut.
Obi-Wan: We go to the royal palace.
GM: It's surrounded by droids.
Qui-Gon: We attack.
Obi-Wan: Do you want the whole army to attack us?
Qui-Gon: Imagine the loot!
Jar Jar: Wesa can sneak in. Mesa knows a way!
Obi-Wan: Good idea, let's go.
GM: You reach a balcony. You see the Queen and her retinue being led away by combat droids.
Qui-Gon: I cast Summon Bigger Fish.
Qui-Gon: I roll 17. I drop it on the droids!
Qui-Gon: Oh wait, no... can I take that back?!
GM: Um... Sure.
Qui-Gon: That'd just be wrong.
Obi-Wan: I concur.
Qui-Gon: It'd stink up the palace for a week. Then she'd never give us a new boat!