In the many reads I've done with The Cannibis Grow Bible it clearly stated to leave the leaves on the plant because it stores sugar which helps the taste. It seems to me I've read it also helps in potency. I tied, mine back in the 8th. week of flowering, but let them go back when I got some good info from Hardon, he said:
While tieing or otherwise repositioning fan leaves is great in veg state, its a break even proposition on flowering, at best.

Each flower pod has a primary fan leaf. This fan leaf does two things.

1. It regulates internal temps of the plant.
2. It is the power plant for that particular flower.

By moving them in such a manner you are literally shutting down or minimizing the power plant for the flower it is designed to power.

So, you may get more light to the flower heads below, but you stunt growth of the flower with the fan you just turned.

Pinning and tieing down the fans is great in veg, as I said. The light gets the secondaries going and it helps develop more branches from which flowers can emerge.

However, the flowers themselves...the individual flower pods, which have the most resin, don't need the brilliant light to continue to bloom. As long as those fans are there in the flower bud, the bud will swell and get fatter and fatter.

Its those fans that power the flower pods to open and reproduce.

Moving the fans so they cannot get light properly, will tend to make them longer buds, but less fat and less hard.

The plant needs it fans and the plant knows where it needs them.

Just some food for thought.
As I said I put mine back and now they're turning yellow and falling off with just a little flick of the finger. If it stays on, it lives for another day.