Many times we tend to make premature decisions just because a generic process dictates to do so. However, early decisions are hugely risky and often result in work that has to be thrown away.
Similarly, if we delay the commitment beyond a limit, then decisions are made by default, which is generally not a good approach to making decisions. That limit is called the last responsible moment (LRM).
Scrum process favors a strategy of keeping all our options open until the LRM, i.e., when the cost of not making a decision becomes greater than the cost of making a decision. See this figure extracted from Essential Scrum.
At the beginning of a development effort is when we have the highest levels of uncertainty. Scrum and Lean Startup processes help us to reduce all forms of uncertainty with validated learning, so that our knowledge about the process and the product grows over the time.
According to the LRM principles, we are delaying commitment as much as we can until we have more information, so that we can make a more informed decision.
-- arturocalvo.com --