Familiars are a valuable addition to a mage's skills. They allow the person in question to be more aware of their surroundings and to perform minor espionage and other tasks. However, they can also be a danger - if the familiar is killed, the mage is in trouble. Some magi eschew familiars in favor of focusing more on their own magic, channeling energy they would be spending on their familiars into other endeavors. The Kirin Tor, in particular, develops numerous other studies that its members can pursue.
The mages in World of Warcraft most closely resemble the focused mage.