The only situation where the HoT is even worth remembering it exists is if the person you cocoon is taking significantly reduced healing, and their bubble wont be popped as fast as it usually does. Which I don't really know of a situation where this exists. The necrotic affix is unforgiving in this because it also erodes the shield and reduces its capacity, making it even worse than usual. Otherwise it's lay on hands or you pad the meters with the shield.