Back in the “old days” downranking spells allowed you to cast spells for the same benefit but at a lower mana cost. Blizzard changed this so that in most cases casting lower ranked spells costs more mana for less benefit. Now there are actually very few spells that should be legitimately downranked. Add to that, with the dual spec options, if you are in your primary spec and you learn an upgraded spell for your secondary spec, the spells on your toolbar for the secondary spec will not automatically update. So it’s easy to accidentally end up casting the wrong version of the spells and doing lower heals/dps/tanking.
By default the addon will whisper the person who casts the downranked spell and record that downranking. It will whisper someone once per 5 minutes per spell. It does it very nicely.. but getting whispers about downranked spells is kind of annoying. You can change the warnings to broadcast to the party (/rankwatch party) or you can change them to not broadcast so that only you will see the warning (/rankwatch none).
WARNING: this addon has gotten me kicked out of one XRealm Pug. It turns out that people get very pissy when you tell them they’re using the wrong rank of spells. Note also, a few people have said that this addon is unreliable when it reports on people cross realm. I’m not sure I believe that. As far as I can tell this is working cross realm.
At this point I have the external notifications turned off (/rankwatch none) so Rankwatch notifies me when it sees a downranked spell and records it so I can check who was downranking later on. With guildies I follow up with them after the raid to discuss the downranking. With other people on/off the realm.. it really depends on how I feel. In one case I’ve gone so far as to log onto another realm, make a level 1 toon, level it up to get 30c (to send mail) and sent them a nicely worded in-game mail about the downranking. That was alot of effort.. and I’m not sure I’ll do it again.