Your 3rd line as a secondary scoring line is ideal, but it requires at least one of your top-2 lines to be able to act as a matchup line. This is of course ideal since your matchup line is going to get a lot of minutes and you'd rather give those minutes to one of your best lines. Fortunately, we have KZB for that which was one of the best matchup lines in the league last year.
In 13-14 our top 6 was:
Kreider-Stepan-Nash
Hagelin-Richards-Callahan
So using the 3rd as a scoring line was pretty obvious. People also seem to forget about 10-11 when we used Wolski-Stepan-Zuccarello as our 3rd line and they had even better results than Pouliot-Brassard-Zuccarello believe it or not.
Incredibly sheltered, but the results were out of this world:
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