Although telling people to the read the documentation can have a therapeutic effect on ourselves, it's not necessarily helpful to the questioner for reasons that may not be apparent to us.  Here are some:

 - Not everyone reads English sufficiently well to make sense of documentation, even though with a couple of examples to get them going they can then figure things out.
 - Even if you are a native English speaker, the conventions of documentation writing which are seem obvious and clear to those of us with a computer science or programming background may be quite non-obvious to those who do not come from such a background (and there are many such users LaTeX).
 - Even if you are a native speaker and have a programming background, some documentation is just plain crappy and hard to understand to begin with.

 And independent of these reasons, if there is a "purpose"  to on the site it should be to be helpful to others on a voluntary basis. So if you don't want to help, don't help, and that's fine. If you want to help, help, don't practice behaviour modification.  For some questions I think it's appropriate to point out that the question is answered on p. *xx* of the documentation, but only as a gentle reminder not as an admonishment.

And remember, as a [wise man](http://tex.stackexchange.com/users/3235/percusse) once described himself "turning the TikZ manual into reputation since 2011" just think of all those points you can get from reading TFM yourself. :)