In my opinion, Running a bias on the LF only covers up a problem with suspension. The reason guys run LF is to stop the LF locking up. The problem is, the LF is only locking up because the majority of the weight is on the RF. This means not enough weight on the LF, and you are essentially overloading the RF. If you adjust the LF suspension so that more weight stays on it, you are using more tire, which equals more grip.
I run my valve on RF for the reasons stated above. cut the RF off and let the LF help pull the car into the corner. Not to mention, with the weight shifting to the RF, the RF will ALWAYS do more breaking then the LF (Check brake temps after a race and you'll see)
Again, just my opinion, and maybe I am wrong. After all, I'm not the fastest guy out there...