Depending on what tactics you use and what mode you go in (10 or 25man) it will differ a lot. You'll never ever press mind sear in 10mans.
I consider it a must do to use a MS/MB rotation when I "stay in" in the ice phase to do as much damage as possible (dot two and spike the 3rd) as fast as I can.
And I'm actually going so far as saying that not using any kind of MS/MB rotation is, if you are not running with 0 mastery. A complete waste of a good 4set bonus.