Considerations

Thus Perseus was equipped - one might even say overequipped - for his task. A quick escape would be essential after slaying Medusa, since she had two equally monstrous sisters who would be sure to avenge her murder, and they had wings of gold or brass which would bear them in swift pursuit of the killer. So at least the winged sandals were a good idea. But if this supernatural appliance guaranteed the swiftest of escapes, why bother with a helmet of invisibility, which made it just about impossible for the Gorgons to find you even if you didn't deign to hurry away? Because it makes for a better myth, that's why.