NPC reaction rolls are great if you have no idea how an NPC or group of NPCs might react to something unusual that the PCs might try to do. You have a table of dice results laid out with entries ranging from "NPC takes extreme offence and immediately attacks" to "NPC approves heartily and gives standing ovation". Of course some of these would scarcely be appropriate for all encounters, and the dice roll should be modified according to the roleplaying situation and exactly how things are handled by the player.

The really good thing about them is that they can generate bizarre reactions that lead the story into interesting directions that it might otherwise not go. Sometimes that can take more adaptability to get out of than simply trying to decide what the reaction is without relying on a table...

Transcript

Mace Windu: {Sally} Am I in time for Jar Jar's big speech?
Yoda: <sigh> Yes, I suppose so...
GM: Go ahead, Sally.
Jar Jar: {Sally} Mesa has muy big news. Da Separatists issa building a biiig droid army!
Senate: <gasp>
Jar Jar: Dis meaning war, wesa needs to have a stronger leader! Mesa suggests Chancellor Palpatine gets emergency powers!
Palpatine: What?!
Obi-Wan: Oooh, no, this is a great move. That's exactly what the Senate should agree on. They don't know about the clone army yet, so they need a unifying leader.
GM: Uh... Okay, I guess. <roll>
GM: The Senate, um... heartily approves.
[SFX]: clap clap clap
Jar Jar: And now, wesa already has a clone army to fight back! Right, Palpatine?
Palpatine: Er... right. I can work with that.