Is It Bad That My Phone Charger Is Always Plugged In?

We've all heard that "overcharging" your phone (aka leaving it plugged in after sufficiently charging the battery) can reduce your phone battery's effectiveness over time. But have you ever wondered about the charger itself? With your cord plugged into the wall (behind the bed, next to the sofa) around the clock, could your charging setup be costing you money or posing a safety hazard?