It can be frustrating sometimes to try and estimate how much a damage over time ability like poison attacks or Ignite will actually do. This can impact decision making: do I need to chase that enemy in order to kill them, or are they already dead? Similarly, is it worth it to try running away, or should I get a few last hits in before I die?
My suggestion is to make a section of the health bar discolored, showing how much health will actually be lost over time before the effect is gone.
Similarly it can be hard to judge the effect of health potions and certain healing abilities. It would be nice to see how much health will be restored from the ability in total.
Damage and healing over time can be added together to show how much health will be left in the long run. There can also be an indicator to show if death is already inevitable.