In the United States, our roads are set up so that we drive on the right side of the road. Slower vehicles are instructed to ride closer to the right side of the road/traffic lane and faster moving vehicles are instructed to pass on the left. The same laws apply to bikes, but there are usually slower than cars, so they are on the right when going straight down the road.
Because roads are set up to assume vehicles are traveling on the right side of the road, a car driver that wants to join or cross a road will first look left, where other car drivers will approach from first. They may forget to check their right. That means if you are riding the wrong way on the street or sidewalk, they might not see or stop for you. So, go with the flow … of traffic.