Now one would ask why write a library that is useful only temporarily? Why not include at once all the parts needed in the final product? There can be several reasons:
- something that is only a part of the scaffolding in one project can stay in the final solution in another one
- the author of the library might not yet fully understand the problem, and it can take years to reach the right abstraction
- the distribution of possibly needed modification can be so uniform that there is no reason to concentrate on one of them more than on another one and it is virtually impossible to cover them all
- and finally: nothing is forever - you never know where a project will go in the future and what you'll need to change
A good example (of the third point) are code samples from manuals - you copy them to quickly get something working - but later you modify it and sometimes you change every character from the original. Another one can be the scaffolding code in Rails - you can debate if it fits the first or the second or other points - but it was useful to a lot of people.
Every library can be used as scaffolding - so why not accept this and help the developers in using it that way?