It is very risky. First, you are driving across town, often paying more attention to the house numbers than to the road. That can result in accidents, especially if you are also extremely tired because you did not sleep well due to excessive time in service. Additionally, using a cell phone to check whether the next call is going to be home or not is dangerous in traffic.
Once you get out of the car, you worry about weather incidents. The Tower is not flexible. You have to dress up to code, no matter how hot or cold it is. And that puts Witlesses at higher risk of frostbite or heatstroke than the average pedestrian in the same conditions. The suit coat contributes to heat stroke, and the collar button done up adds to it. In very hot conditions, you want loose, light colored clothing (white shirts work best here at reflecting heat). Having a suit coat on top of a white shirt defeats the purpose of having the white shirt (solely because it reflects solar energy best). In cold weather, a dark coat on top is recommended, and sisters need pants or leg warmers in very cold weather.
One thing, besides crime, bad steps, and dogs that you worry about is what about that householder that is coughing nonstop. Is that the flu or bronchitis, or is it tuberculosis? People that go door to door, especially if they do not sleep well, are prone to picking up these infections. I wonder how many times someone has gone to the door, healthy albeit tired, and picked up a cold or the flu that way. And people can spread colds and flu, and tuberculosis, among car groups. You can spread a cold before you even know you have it, and often this results in spreading it around car groups and to other householders that were healthy before you showed up.
Finally, this is one risk that is commonly forgotten. When we bring children to the doors all day, we deprive them of the chance to play and learn. Remember, many toddlers are born scientists and thus are into everything. This gets suppressed when they have to spend the better part of the day out in field circus. And this leads to stagnation that is extremely difficult to remove later in life. Such children never get the chance to develop properly. Spankings and after-service punishments add to this, since children are not supposed to be following their parents in door to door work all the time. This is true regardless of how otherwise safe the area is, and is not a hazard with Halloween because that only happens once a year and for a couple of hours at most. Field circus is all day, every day, and that's when it displaces learning.