So the question is as follows: what could you lose? Now, I'll be talking a lot about shaman abilities specifically here, but I'm hoping that the reasons I'm giving could apply to your class too.
I can't pretend to know all the classes inside out, but I suspect that there will be issues that apply to everyone.
The little-used
So this is an obvious place to start.
If you don't much use an ability then it can probably go, right? Good examples for shaman would probably be things like Far Sight or Bind Elemental. But those things have their uses, too.
For example, I use Far Sight all the time in PvP, especially in battlegrounds like Eye of the Storm, where it is really well-used to keep an eye on other bases or the flag. I also use it to get screenshots quite a lot!