Shields and status resists are interesting things.

I use a Horned Owlite Shield, which possesses Shock resistance. In situations where I'm shocked (too goddamn often) I utilise my shield until it wears off, and find that instead of shock damage hitting me for a full bar of health, it only knocks off half a bar instead when it acts while shielded.

Status resist is a funny thing. For some statuses like Fire, Freeze and Shock which do damage, you'll find your resistive shield reduces to negates damage from the status, though secondary effects still apply. The same principle would work with the other statuses, which all have secondary effects only: Stun slows you down, Curse damages you on using an item (which shielding can't stop due to impossibility of attacking while shielded), Poison reduces your physical prowess and prevents healing while Sleep disables you. The secondary effects of the other three statuses are on top of the primary effect, damage, which in this case is stopping action in the case of Shock and stopping movement in the case of Freeze.

While shielded in a status trap, you'll find your shield resists the effect from occurring until it breaks.

In summary, status resist on shields reduces primary damage from statuses when shielding and reduces the chance of status infliction from traps and monsters on top of blocking damage.