The second question also came uo over at Totem Spot and Bink and Haarne answered as followed:
Always Be Casting! Not using procs because of a second proc while LvB is already off CD may feel like you lost something, but if you tried to stopcast, you will at least loose a whole GCD and whatever time you were already casting. Thats even worse than not using one LavaSurge proc.
Here's the thread over at TotemSpot
Lava Burst
Regarding your first questions, I can only assume it might be a DPS gain for one or two adds, if you are not able to cast CL. If you would do that, you might lose to many Lightning Shield stacks by not using Eart Shock, but I'm by no means sure about that.