When determining the future state there is always the ideal future state and the real or pragmatic future state.
The ideal future state is the future state if there were no constraints. Constraints could be financial, people, time and effort, and any number of change management issues.
The path to the future state is not always a straight line
The roadmap from the current state to the future state may be long and complicated.
Analyzing the gap is key for determining what the go-forward plan is. The gap contains everything that may be affected by the change. There may be many future states on the road map prior to the ideal future state being realized.
Keeping the ideal future state in mind helps guide what the roadmap will look like.