Benefits.
The definition of the objectives of your project allows you to reach a clear and common understanding of its realisation with your sponsor(s). This will also enable you to effectively plan your project and keep your team focused.
When to apply?
After having investigated your project context and before any planning activity.
How to?
Define your SMART final objectives and identify the intermediate ones. Draw their dependencies on your Project-Cone© and allocate a date to all of them.
Specific - Measurable - Achievable - Realistic/Relevant - Time-bound.