If you move zero, but did not specifically forfeit your movement, you still advanced (and thus, can still change facing, which is part of an advance). This would still trigger Sentry, for example, since:
Quote Originally Posted by Sentry
When an enemy model advances and ends its movement in the LOS of a target friendly Faction model, the affected model can immediately make one normal ranged attack, then Sentry expires.
If you forfeit your movement to aim (which any model can do; even those without ranged weapons), you will not have advanced, but still end your movement:
Quote Originally Posted by Prime, p. 65
When a model forfeits its movement, resolve the effect to which the movement is being forfeited, then the model ends its movement, triggering any relevant effects.
komt er op neer dat een model zonder ranged weapon toch kan movement opgeven om te aimen en dus geen advance doet, en zo kan je elk effect dat zegt "When an enemy model advances and ends its movement..." omzeilen.
