The problem with leveling efficiently in World of Warcraft is not in what quest to do when, but rather it's how you level that's important. For example typical game play follows like this. You're attempting to power game your way through a particular zone or finish a series of quests. Somewhere along the way you get stuck so what do you do? Most people Alt+tab over to your trusty leveling guide or over to thotbot look up the information they need and then Alt+Tab back into the game and carry on. While this may only take a few moments to do, you are in fact wasting time. If you were to keep track of the total amount of time you wasted by Alt Tabbing over the span of say several levels it can quickly add up to a huge amount of wasted game time.
This is where the Team iDemise leveling guide shines because it eliminates the need to Alt+Tab. Instead this guide site inside your game. When this guild created the guide they affectionately termed it the iDemise Map Mod because in effect that's exactly what it is. The entire leveling guide site inside your game and you have complete access to everything you need to level efficiently without ever having to Alt+Tab again.