Are Third Party Candidates Just Spoilers?

[Machaut]

At the conclusion of the primary, I had a feeling the general election would see a close Hagan victory over Tillis. As we approach election day, it appears that may be the case.

Hagan continues to lead close NC Senate race - Public Policy Polling

PPP's newest North Carolina poll continues to find Kay Hagan in the lead, although the race has tightened slightly compared to a month ago. Hagan is at 42% to 38% for Thom Tillis with Libertarian Sean Haugh continuing to hold on to 8% of the vote. Haugh's supporters say they would support Tillis 61/19 over Hagan if they had to choose between the two major party candidates- when you allocate them to their second choice Hagan leads by just one point at 43/42.

So, in general, what really is the purpose of third party candidates in America's elections system? Aren't they just spoilers?

Many, however, cast their votes for a third party candidate, even though they know s/he won't win, simply because they refuse to continue voting for the lesser of two evils. Are you one of these people?