Literary critic: Often the heirs of a successful writer decide to publish the manuscripts and the letters the dead writer left behind, regardless of the merit of the work  However, many writers have manuscripts that they judge to be unworthy of publication and with which they would not like to be publicly associated even after they die
Hence a successful writer who decides not to publish a recently completed manuscript should destroy it immediately
Many posthumously published books would have been published by the author had the author lived.