I facilitated the Casual Constraints Contest during 2 events. I would really recommend this technique because of the big play-factor in it! The participants are challenged to come up with as many ideas as possible, give to some constraints.
Because of the competitive aspect in this techique, I discovered that competitiveness plays a large role for many participants. In both sessions, we came up with a lot of creative, unusual and executable ideas!
Use this technique when you have to overcome constraints or when you just like the more play-wise way of facilitating but still want a usable and serious outcome.