A way of having your cake and eating it.
In a fast-changing world there is a tendency for two things to happen:
1. the organisation becomes extremely short term
2. the organisation stays long term in its vision but systematically fails to execute it
Chunking is the best way of ensuring that long term goals and vision are achieved with the minimum amount of risk.
It is a way of maintaining people's interest and commitment on a long project by ensuring appropriate, early and sustained wins.