I always use the sidewalk when biking (legal in my area), but, besides the law, I can see some arguments against it. For one, many sidewalks are in bad repair, so if you have a bike designed for the flat surface of a road, a bumpy sidewalk can be a problem. I have a BMX-style bike, so no problem for me...the bumps are fun.
Another point is, even if it's a nice sidewalk, you generally can't go as fast as the road because of the danger of running into pedestrians and other random obstacles like fire hydrants, telephone poles, etc.
Yet another point, is that I hear very frequently that it's statistically safer to ride on the street. I haven't found a solid source for this though, so maybe it's not true. Or maybe it's true for a certain style/attitude of biking that doesn't apply to me. In my town, I certainly feel much safer on the sidewalk. Perhaps I have a higher chance of a minor injury on the sidewalk, but I will take that over a lower chance of getting hit by a car.
Generally, my attitude while riding is that I'm a pedestrian who can move a little faster than walking-speed, not an automobile that can move a little slower than driving speed.
Another point is, even if it's a nice sidewalk, you generally can't go as fast as the road because of the danger of running into pedestrians and other random obstacles like fire hydrants, telephone poles, etc.
Yet another point, is that I hear very frequently that it's statistically safer to ride on the street. I haven't found a solid source for this though, so maybe it's not true. Or maybe it's true for a certain style/attitude of biking that doesn't apply to me. In my town, I certainly feel much safer on the sidewalk. Perhaps I have a higher chance of a minor injury on the sidewalk, but I will take that over a lower chance of getting hit by a car.
Generally, my attitude while riding is that I'm a pedestrian who can move a little faster than walking-speed, not an automobile that can move a little slower than driving speed.