According to PMBOK, “The project beneﬁts management plan is the document that describes how and when the beneﬁts of the project will be delivered, and describes the mechanisms that should be in place to measure those beneﬁts. A project beneﬁt is deﬁned as an outcome of actions, behaviors, products, services, or results that provide value to the sponsoring organization as well as to the project’s intended beneﬁciaries”.
This document is a living document and according to me, its life-cycle starts way before any business plan is laid out. Information exists for this but maybe not in a centralized place. Many factors such as business execution environment changes (evolution, devolution or revolution) and/or strategy, management and economy changes are the ones which trigger activities that generate a probably viable business sustenance/execution plan.
Formation of a project and/or group of projects/programs comes way later in the picture. Risks, assumptions, and timeframe for benefits realization are the most important key elements that shape a project and/or program. Investments and ROI of a business proposition play a very tangible role in idea generation which later based on other factors can lead to project ideas and/or planning of benefits realization.
Needs assessment and business case generation/analysis comes at a later stage after the investment model and ROI generation has been effectively strategized. All big companies including start-ups take this very effective approach to project initiation. In practice, I have seen the business case and project benefits plan going out of sync even though the strategic owners of both of them are more or less from the same organization. At times, both of them will be creatively used to influence a go-no-go decision on a project and/or make-buy decisions.
In general, if a project slips the implementation timeframes, the timeframes for benefits realization also slips. And at times, business case might make sense in a long term strategic perspective but the immediate benefits realization might get hampered and become invalid. Personally, I would prefer if the strategic owners of the business plan and benefits realization plan are in sync with the project sponsors. Project manager, in this case, is a mere executioner with very little control on the external factors. What is your view?
 Project Management Institute (2017). A guide to the project management body of knowledge : (PMBOK guide). Newtown Square, Pa: Project Management Institute, p.33.