ObjectOneOf subClassOf/equivalent

Hi,Please, can you clarify for me these points:Can I add an axiom to an ontology subClassOf( X ObjectOneOf(x1 x2 x3) : in each real case can I apply it?It isn't better to add equivalentClasses( X  ObjectOneOf(x1 x2 x3) ,I remarked that each one of them close the world? Aren't they? Is there a case where we have to add the first axiom rather than the second?thx