[spondyl]

> I've never done it, and I don't know why I'd do it.

The original waterfall paper[1] advocated for doing an initial version, by which point you'll have understood the problem domain (in miniature) enough to make a better attempt by throwing it all away and reassessing what tradeoffs make sense.

> Without this simulation the project manager is at the mercy of human judgment. With the simulation he can at least perform experimental tests of some key hypotheses and scope down what remains for human judgment, which in the area of computer program design (as in the estimation of takeoff gross weight, costs to complete, or the daily double) is invariably and seriously optimistic. [2]

The myth goes that someone in the Department of Defense looked at the first diagram (which the author claims right underneath is flawed), copied it in a rush for a diagram and that became enshrined in history as "How best to develop software" until agile and what not

[1]: http://www-scf.usc.edu/~csci201/lectures/Lecture11/royce1970... [2]: Page 7 of the above PDF