Butchering is one of the 4 Gathering tradeskills in WAR. Butchering allows you to gather from animals rather then humanoids. Items that you can butcher from animals are used mostly for Apothecary and Cultivating. Scavenging on the other hand can be used for both Tradeskills. The thing here that would compel someone to go Butchering is well... Someone's gotta do it. If you're on a server like mine Butchering is actually better due to so many people going Scavenging or Cultivating over it.
As a Butcher your main source of income will be from Nutrients, The Nutriment category consists of (Guts, Gore, Blood, Lifeblood, Gall and Viscera.) If you want to go Butchering for money I highly recommend you change your mind, since they have far less things they can sell for profit. If you get lucky (Like on my server) then you would actually make more then a Scavenger. Check the auction house and see what sells the best on your server. Then make your choice.
Some Butchering ingredients can only come from certain species. Here is a list of the rare Butchering Ingredients that can ONLY be found on these 4 species.
Boar Blood - Boar
Manticore Fang - Manticore
Horse Leeches - Pegasus
Ribbon Leeches - Unicorn
As with Scavenging the level of mob depends on what level loot you will get when butchering them. Here is a quick reference table for you;
1-10 Mobs 1-50 Loot
11-20 Mobs 51-100 Loot
21-30 Mobs 101-150 Loot
31-40 Mobs 151-200 Loot
Here are a few links to helpful things on the Butchering Tradeskill;