Unlike an Elemental, however, the Infernal can be controlled with traditional pet commands but has no special abilities. Used purely for amusement purposes as the standard pets perform better in most situations, it gets even more left behind in Wrath of the Lich King as there are no new talents or abilities that make it more useful.
Using the Inferno spell also costs a reagent, the Infernal Stone, which costs 50 Silver. Other than entertainment in the Battlegrounds and outside Auction Houses, there's little purpose to using the Infernal. You can theoretically use it against numerous mobs, but also remember the 'only usable outdoors' restriction. The only good thing about this particular demon is that it is a 1.5 second cast (down from 2 seconds) AoE stun.
While several talents in Demonology increase the pet's effectiveness -- from Stamina to Intellect to Critical Strike chance -- it benefits from no special effects from talents like Demonic Empowerment or Master Demonologist. Furthermore, the 5 minute duration and being prone to diminishing returns on Enslave Demon make this demon less of a useful pet than it is one of the Warlock's best parlor tricks.