As I said, jcl stated this somewhere here. I'm afraid I've never tried it myself yet. My guess is that, for example if you're using a water shader which uses material skills to determine flow speed or something similar, you'd have to attach to the model a simple action that reads like this
Code:

---

action whatever
{
  theMaterial.skill1 = float(someValue);
}

---

in order for the material skill's value to be converted to floating point. As far as I know, shaders can't use fixed-point vars which, in this case, would cause the shader not to function properly.
Another example: If your shader uses material skins, you'd probably need an action which assigns the proper material to the model. Otherwise the shader won't have a clue about which material's skin to use.
All this is just guesswork though, if I were you I'd maybe PM jcl so he could explain this in more detail...