Again, if Warrior functioned exactly the same, and IB was shield rather than a heal, it would still be perfectly fine to use it reactively. Other than healers perhaps not seeing that you used it, vs a healing-IB, it still would give you the same amount of health-post action. It just means that if 2 cure IIs hit you at the same time and cap you off, or near it, you get more out of a IB-shield than an IB-heal.

To be honest, you'd probably still want to use it reactively, rather than rotationally, because the loss of wrath stacks counts for something.