We use MBIs as the core of our planning event instead of epics or features because computing Weighted Shortest Job First (WSJF) on either epics or features does not provide an effective ordering. Epics are bigger than the actual work we will implement. Hence, doing WSJF on an epic doesn’t really make any sense since some (most?) of the epic will never be implemented. Rather an epic can be thought of being a container for the features we will be creating.
But features, by themselves, often provide no value. Features, even when having no technical dependencies on each other, often have business dependencies on each other. This means that features often do not represent any value in and of themselves – that several features are required to deliver value. When using features as the increment of value, teams often find they have to de-scope the features during the planning event to find the subset of the features that are needed in the time frame allowed. We have found it more useful to create MBIs from our epics and then do WSJF on them. Then, during the planning event, we already have the focus we need on the features to build. That is, we define our features within the context of the MBIs from which they spring. This makes de-scoping during the event unnecessary – we’ve in essence already done this. MBIs get us focused on both our target market and the minimum business increment we can deliver. A focus on business value is a powerful thing.