write callbacks and Stdio.File.set_buffer_mode()

[Marcus Agehall (nu med K-m�rkt fastighet och ny elcentral) @ Pike (-) developers forum]

If I set a Stdio.File object to buffer mode with both an input and an
output buffer, is there a point in having a write callback registered?
I can simply output data to the buffer and it will be written to the
stream, right?