Most people think of Deo-S as a hazard lead and usually try to set up on it just to be promptly KO'd by one of its amazing coverage moves, with Psycho Boost obliterating anything that doesn't resist it.

95 SpAttacking stat isn't terrible, and is helped a lot by LO or even Specs. With its 180 Speed its essentially like holding a Choice Scarf without the Choice part.

It's pretty underrated and acts as a solid revenger.

252+ SpA Life Orb Deoxys-S Psycho Boost vs. 4 HP / 0 SpD Dragonite: 263-309 (81.1 - 95.3%) -- guaranteed OHKO after Stealth Rock
252+ SpA Choice Specs Deoxys-S Psycho Boost vs. 4 HP / 0 SpD Dragonite: 303-357 (93.5 - 110.1%) -- guaranteed OHKO after Stealth Rock