When kids are being disciplined, having a choice helps facilitate the idea that their back is not up against the wall yet (figuratively). The fight-or-flight instinct hasn't been touched off yet. When I used to teach in an alternative high school, if I wanted a student to do something, I'd give them two options, even if I knew they didn't want to do either of them. Usually, that was enough to move them at least closer to the objective of the lesson, even if it still wasn't perfect. Today, when I have students that are (I'll just make up a quick, implausible example here), on Facebook or Youtube when they should be working, I tell them to close it. If they don't, the next step is "You close it, or I close it." (To most kids, keyboard shortcuts are still a total mystery. I tell them it's magic :-)) Generally, they'll start moving to close. All kids want is to feel like they're not on a one-way street.
In terms of curriculum, whenever I'm designing assignments for regular classes or my technology classes, I do everything in my power to incorporate choice into the project. When I can do this, everybody is happier, me included. For instance, my 8th graders are currently working on a project about the Vietnam War on Glogster. I gave them a list of things to include, and they chose 3-4 in each category. Added bonus: they get a big long list and are overwhelmed, and then I tell them they don't have to do it all :-) My 7th graders are making interview videos in iMovie about technology and how it impacts us. While they didn't have a choice on the general topic, they can choose the specific question they are asking people, and then can choose what the final product looks like.

[Note: all the links in this post are how these tools relate to education.]