This is a simple WA to help with the WW single target rotaion. You should aim to use the left-most icon, while the others will show you what's "coming up".
This WA is very naive, and is just a copy of the Rotation Priority on wowhead. As such, you may see multiple Icons appear from time to time (e.g. 2 Tiger Palms). This probably does not mean you should cast multiple of the same spell in a row, since you would not want to ruin your Mastery / Hit Combo.