It is safe, in fact this is a way of switching off in an emergency - holding down on/off switch for four seconds.
But I would not recommend regular use to switch off - better to just be patient, or to investigate why switch-off is taking so long.
Alienware 17 R4 2017 review
These brilliant Lego posters show just what children's imaginations are capable of
Mac power user tips and hidden tricks
Comment réinitialiser votre PC, ordinateur portable ou tablette Windows ?