This strategy makes sense in battleground states but what about in the opposite case (say hawaii (very D) or wyoming (very R)) - I'd argue that by voting for the third party candidate is the better option as you are unlikely to change the outcome of the election one way or the other - but you reduce the mandate of the winner that you are less aligned with, and by marginally improving the showing of the third party, make it more likely that mainstream candidates will want to address issues of concern to a newly visible voting block?