As most people have already said, Skinks greatest assets are their mobility and flexibility. They're generally poor melee combatants, and they'd be turned into a bloody mist by any proper melee force like Khorne troops or Ogre troops, but the whole point is that they're never supposed to be in combat for any length of time (Which is why boltsplitters and shields are our most popular weapon combination for basic skinks). Even if they do get caught, they're surprisingly resilient with their Star Bucklers, and they can pull out of combat easily. Whats more, as with all of our models, they have impressively high leadership, way higher then most chaff units, like skaven. They can take objectives quickly, screen others units, and are generally just really useful generally, which can be good in a competitive setting where you may need a model to serve in a large number of roles.