When to use Mind SearFollow

Hello fellow priests,

After a 8-month break I returned to WoW two weeks ago. I leveled my priest from 70 to 80. In general I'm doing fine as shadowpriest (I think...) but with all the changes in the past half year, I'm still full of questions. And most guides I found, are a bit outdated.

So... Can someone tell me when to use Mind Sear? I noticed it's fun on the zombies in Stratholme. But on what occasions should I use it? On groups of trash mobs in instances for example?

Also, I'm curious how to deal with fast-dying mobs nowadays. Is dot-ing them a waste of mana? And how to max my damage on them? This weekend I did some heroics, did fine on the bosses but I feel like I could do much better on the trash.

Thnx for any help.

I don't know the details, but if you know roughly how much DPS Mind Sear does on each target. (simply divide the damage per tick by the number of seconds between ticks)
Then you know how many mobs you need to pass your single target dps and thus when you should or should not use Mind Sear.