Originally Posted by Onodrim

About Envenom clipping: When you perform an Envenom, you recieve a buff called Envenom that increases your chance to apply Deadly Poison by 15% and your chance to apply Instant Poison by 75% for 1 second plus an additional second for each Combo Point used for that particular Envenom. That means you recieve the Envenom buff for six seconds if you perform a five Combo Point Envenom. If you perform another Envenom before the Envenom buff has run out, it's called clipping your Envenom buff. This isn't normally a problem, bar situations with BiS, or near-BiS gear, or in situations with increased Energy regeneration.

About Bloodlust/Heroism: Bloodlust increases your attack speed for 40 seconds. This will, all things being equal, increase your number of critical strikes in that time span which, in turn, will increase your Energy regeneration through Focused Attacks. Overkill also increases your Energy regeneration, and stacking both of them (Overkill and Bloodlust) will naturally increase your Energy regeneration even further allowing for more Mutilates and Envenoms. This can be a good thing, but not if it leads to Energy capping. Add to that: It can also be exactly one of those situations where you might experience Envenom clipping, which, generally, is sub-optimal (unless you'd otherwise cap out Energy).