M.L. West, Hesiod, Theogony: Edited with Prolegomena and Commentary
(Oxford: Clarendon Press, 1966) p. 277 (on Hecate, lines 404-452):
We are accustomed to think of the ancient gods in pigeon-holes: Hephaestus as the god of fire, Poseidon as the god of the sea, and so forth. In reality they can very seldom be summed up so neatly. A god's functions are as wide as the needs of his worshippers. Every town, every social or professional group, every family, generally has one principal deity whom it worships above all others; and the demands of that band of worshippers, in so far as they are not answered by other gods, will determine what different faces the principal god's predicated power will assume.