For a while I have been using the following macro for my destro lock:

Code:
/castsequence reset=10,target immolate,,incinerate,,incinerate,,incinerate,,incinerate,,conflagrate,
/cast chaos bolt
/stopmacro [target=pettarget,exists]
/petattack
The idea behind the double commas in the castsequence is for it to try to cast chaos bolt at every opportunity, and move on if the cooldown wasn't ready. After observing some odd behavior, I decided to try the following macro:

Code:
/castsequence reset=10,target immolate,incinerate,incinerate,incinerate,incinerate,conflagrate
/cast chaos bolt
/stopmacro [target=pettarget,exists]
/petattack
Notice that in the second macro, the double commas have been removed. Remarkably, the second macro showed the exact same behavior as the first macro. You wouldn't expect it to, but the second macro attempts to cast chaos bolt at every opportunity, but casts spells from the castsequence if chaos bolt is still on cooldown.