During the Release Planning phase of a project we usually estimate and prioritize the MSL (Master Story List), also called Product Backlog in Scrum. The output of these exercises is a Release Plan which contains a vision of Time, Cost and Scope of the project. This phase usually happens for the first time during the inception, before the project starts. It needs, of course, to be constantly reviewed and recalibrated in a more fine grained level of details once the project is underway.

One of the main things we need to keep in mind at this time is that these are ballpark numbers.

Definition of Ballpark: A good numerical guess; an estimate.

 

In order for the decision makers to have an idea of these three variables (Time, Cost and Scope) and then make a decision whether to start the project or not, taking into account mainly ROI (Return on Investment). Most of the time they need these numbers for budget approval so that the project can start. The numbers are not precise at all and they will change for sure when the project starts. But as I mentioned before, they are an estimate, something close enough to the real numbers.
We should only spend enough time to get to a comfortable stage where a decision can be made to take the next step.

One of the clients I've been to had a very good way of deciding about funding approval according to the output of the release planning. They knew the numbers were not precise so they had a form with:

How long is the project going to take?

• 1 to 3 months
• 3 to 6 months
• More than 6 months

How much is the project going to cost?

• 10K to 100K dollars
• 100K to 500K dollars
• 1M to 5MK dollars
• More than 5M

The main point is that it's useless to try and figure out whether the project will take 30 or 35 days at this time, of course we need funding and budget allocation, but nothing stops us from allocating X amount of money, try it and then continue if it works.

"Don't aim too much before shooting, shoot and then adjust and then shoot again and adjust..."