You have to be simultaneously well-prepared and spontaneous. You don't really know for sure what percentage of the preparation you are going to use, and you don't know exactly where it will apply. So you have to be prepared, but not locked into that preparation.
A riot is a spontaneous outburst. A war is subject to advance planning.
It's hard to be spontaneous when you have 40 people in your crew, and you're playing to 16,000 people every night, and there's giant lighting rigs, it's hard to change direction on a dime.
Occasionally if you do something extraordinary, the crew responds with spontaneous applause, but that's very rare.
Spontaneous combustion of grassroots politics is the future.
The better organized you are in the simple things, the more spontaneous and free you can be in the ore important things.
Creativity comes from spontaneous meetings, from random discussions.
The sophisticated concern about art sinks before a spontaneous love of reality, and I thank the photograph for being so transparent a vehicle for things...
I am the most spontaneous speaker in the world because every word, every gesture, and every retort has been carefully rehearsed.
I've always been quite a spontaneous person, so I would lean more towards, if you feel it and you know its right, then do it.