Why pitch yeast in secondary?

[Kironosaurus]

I am looking to make a Brooklyn Sorachi Ace clone and their website mentions adding a champagne yeast to the secondary. If the beer is done fermenting before racking, why would adding another yeast benefit the beer? Are there sugars that Wyeast 1214 won't eat that but WLP715 will? Should I make a starter for either yeast? Maybe the lack of a starter will produce esters that may be beneficial?

Here is the BIAB recipe I am using:

Batch Size:5.00 gal
Boil Size: 6.25 gal
Boil Time: 60 min
Efficiency: 63.00
IBU's: 34 IBUs
Est. SRM: 5 SRM
total hops: 7 oz
grain wight: 13 lbs
Pre-boil grav: 1.056 SG
Est. OG: 1.068 SG
Est. FG: 1.011 SG
Est. ABV: 7.4 %

Ingredients
13 lbs Pilsen Malt 2-Row
1 lbs Cane Sugar
.5 Oz Sorachi Ace [11.7 %] - Boil 60.0 min
.5 Oz Sorachi Ace [11.7 %] - Boil 30.0 min
2 Oz Sorachi Ace Leaf [15%] - Flameout

1 pkg Wyeast Labs #1214
1 vial White Labs 715 Champagne Yeast - Add in Secondary
6 oz Sorachi Ace leaf hops - Dry Hop 7 Days

Mash
Mash Steps

122.0 F 10 min
146.0 F 60 min
152.0 F 15 min
Mashout 168.0 F

Thanks everyone.

 

[NordeastBrewer77]

I'm guessing the recipe says to repitch the champagne yeast so that that yeast is the one that does the bottle conditioning, it's cleaner than the Chimay strain you'll use to ferment. The champagne yeast may also ferment the beer down further than the Belgian strain (a winemaker would know WAY more about this than I, that's for sure), but I'd guess it's more for bottling than anything else. You could probably skip it, but it won't hurt.
I'd definitely make a starter for the initial pitch, I always make starters with liquid yeast unless it's a small, lower gravity batch. As for the champagne yeast, I don't believe it's as important to make starters with that type of yeast (again, a winemaker would know better than I), but I'd personally still do it.

 

[Kironosaurus]

Thanks for the info! Hopefully the WLP715 will further ferment the batch as well. Calculating a FG of 1.017 with the Belgian yeast, but would prefer a FG around 1.010 or under.