I down voted because although I think what you are saying is common parlance, it is really, really bad advice and mixes up causality. Projects which both do their job and are this well documented attract developers, both to maintain and reuse. Look, for example, at everything done by Armin Ronacher, or at SQLite.

And writing documentation only seems like a waste of time to the developer who just finished writing the code. It wastes their time. But spending time now to write good documentation saves the organization as a whole much more of other developer's time in the long run. It's a smart investment to make, even when the collateral damage is time wasted documenting code that really is thrown out.

(But, if you actually document the code well you'll find out that you throw things out much less often.)