Electric Kettles offer a lot of advantages over their stove top counterparts.
Efficiency - Electric kettles are by far the most energy efficient way to boil water. Boiling water in an electric kettle is 81% efficient, followed by the microwave, at 47% efficient, and the stove at 30.5% efficient (source).
Temperature Control - Most electric kettles have a build in thermometer to control the temperature of water. This is important for brewing different kinds of tea (Especially green and white).
Safety - All Electric kettles have an automatic shut off feature. This means even if you forget about the boiling water, it will not boil away and potentially damager your kettle, or worse!