Please excuse my French but I could not resist the pun!
Agile proponents, including me, often use an improved return on investment (ROI) as an argument for avoiding traditional software development methodologies in favor of agility. The scope considered for this ROI usually concerns the financial investment made for the particular project and the result the stakeholders are expecting from it.
There is another ROI that I think is important to consider and that is also heavily impacted by the adoption of agile practices: the intellectual return on investment.
Indeed, developers involve a lot of themselves when working on a software project. The most obvious investment is the time spent at their desks but there is also a tremendous part of the job that is done after hours, outside of the office.
Ever zombie drove from work while mentally exploring the arcane of a new system's architecture? Ever had the light bulb that turns on while revisiting the latest written code under your shower? If yes, you probably see what I mean when I say that software development is pretty mind invasive.
Pecuniary compensation is often considered as the just compensation for this invasion: I pretend this is not enough. Money only buys time. The intellectual investment must be compensated by a specific ROI. What could be this specific ROI?