Rdfs:label vs. skos:prefLabel vs. dc:title

I've seen some datasets that use all three of rdfs:label, skos:prefLabel and dc:title to name the same resource. Is this good practice? And why would there be three, almost identical "standards" for labeling a thing; surely this is an obstacle standing in the way properly exploring linked data since a user would have to know which of the three is being used before being able to conduct a useful query?