Although I often preach an agile approach to developing software, the planning cannot be neglected altogether. Planning is needed by stakeholders to make decisions about various activities connected to the software, like marketing, deployment, education etc.
I don’t remember who first said:
“Planning is everything, plans are nothing”
And the agile manifesto says something similar:
“…Responding to change over following a plan”
What I’m trying to tell you is that planning is a continuous activity, while a plan is a snapshot of a particular moment in time. Planning is an iterative process while the plan might be outdated the moment it is done. The further into the project, the more information you get and the more accurate the plans will be.
This also implies that plans stretching far into the future are more unreliable than those trying to tell a near future. Also see my post about the horizon of predictability.
Far too often project managers stick with their original plan although the reality that was once the basis for the plan changes. Commitment is good but being adaptive to changes is better. Don’t neglect planning, but don’t rely on your plans.
Read more about agile planning in Mike Cohn’s excellent book: Agile Estimating and Planning.