Taras (Roman Tarentum) was a true colony of Sparta, founded as the result of a decision of the polis of Sparta, traditionally in 706 B.C. Taras was the name of the legendary founder, a son of Poseidon, who is depicted on coins and in art (sometimes indistinguishably from Arion) riding on a dolphin's back. If the inhabitants of Taras had requested help, it would be obvious why the Spartans would have gone to their aid. Samos, however, was not such a colony, yet when a Samian delegation arrived at Sparta asking them to help them get rid of their ruler, the tyrant Polykrates, the Spartans agreed.
Read more about Samos and Sparta.
Photo of Salt Factory Ruin at Samos by Melilab at Flickr. Creative Commons License.