Raising your nocking point can alter the tuning of your bow. The higher you go, the lower the spine that will tune. You are losing energy input to the arrow when you do it. You also introduce another force vector to the dynamic spine equation, and if you're not perfect in your form or release it has more effect. I wouldn't do it- do as George said, and use some spray on the fletching.
Hunting in the rain plays hell with blood trails... I don't do that either, unless there's just no choice.