You'd be suprised at how often it actually happens - someone in your group is using the wrong rank of a spell. Like I mentioned about healing a couple of posts ago (Holyness, what's it all about), there was a time when downranking spells was the skilled way to go about things. Some changes from Blizzard quickly made downrankers go from leet to noob however, and although these changes were implemented quite some time ago (with the coming of wotlk I think), people still downrank their spells. Why is this?
First of all, there are actually still good reasons to downrank spells. Sometimes you want a lower rank because it is less good than max rank, like with Life Tap and Health Funnel for warlocks which drain less health at lower ranks. Mages might want to use rank 1 frostbolts when pvping because it has faster cast time but is still as able to proc the snare effect. Similar downranking reasons exist for many classes.
But most of the time a downranked spell is simply a mistake. The most common cause to this mistake is dual speccing. Some time ago, before wotlk, you had to place your new ranked skills on your bars manually everytime you bought new ones. Blizzard changed this so that the bars would automatically update with the latest rank when you bought it, and this led to people assuming they'd always do this. But they don't. If you're dual specced and buy new ranks of your other spec, the one you're not currently in, the bars won't update. But people still assume they do and don't even check. This has happened to me too, embarrassingly enough. I had the wrong rank on nearly all my paladins threat skills. Wonder how I've managed for so long. Only for one rank, but still.
Nearly every pug I join has at least one player using at least one spell with the wrong rank. And this is where the addon Rankwatch comes into play! It checks the ranks of all the spells used and tells that player, by whisper or in party/raid chat that they're using the wrong rank, and which rank they should be using. It doesn't report for spells commonly downranked, like Life Tap and Health Funnel I mentioned earlier. I've enabled it to tell people in party/raid chat simply because I think everyone in the group should know someone is using the wrong rank of a spell, encouraging them to correct the mistake faster.
The addon can be found here --> RankWatch