Unless you live in a swing state, how is voting 3rd party "wasting your vote"?

Your vote won't "count" anyway. There are only about a dozen true "battleground" states - if you prefer Nader or Barr and live in Utah, Texas, Mississippi, or New York, Vermont or Machusetts, why wouldn't you vote 3rd party? How would that be "a vote for the other" major party candidate? It's an electoral college and we know who will win those states.