This is currently a double ended discussion.
Point 1) If L&L procs and you are coming close to capping focus, Cobra Shot would lead you to cap focus faster, and in this situation Kill Command and Serpent Sting are the only 2 bleed off shots.
Point 2) With a 1 sec GCD you can now add shots into a L&L proc after the GCD has finished to make use of that time. If L&L procs and you ARE NOT immediately going to cap focus, you have the option to use Kill Command, Cobra Shot, or Serpent Sting as the filler. This is not directly the "Oh I need to use some of this focus" really, its "WTH am I standing here when I can use this GCD for something."

Both points have to be balanced, that's why he said it is more complex.

@Frostheim - Do we know if Cobra Shot is functioning like Chimera Shot as far as +dmg/+crit vs +AP during Serpent Sting refreshing? Extending that, is it possible for a MM hunter, if your focus management got off and you realize 2-5 seconds before Chimera is off CD that you won't have enough focus to refresh the sting before it falls, could you cast a Cobra Shot in a pinch?