If you're going to build a $10 million skyscraper, by all means, plan and prototype and discuss and plan some more.
On the other hand, if the cost of finding out is a phone call, make the call. No need to spend a lot of time planning how to call or when to call or which phone to use when execution is fast and cheap.
The digital revolution has, as in so many other areas, flipped the equation here. The cost of building digital items is plummeting, but our habit is to plan anyway (because failure bothers us, and we focus on the feeling of failure, not the cost).
The goal should be to have the minimum number of meetings and scenarios and documentation necessary to maximize the value of execution. As it gets faster and easier to actually build the thing, go ahead and make sure the planning (or lack of it) keeps pace.