Following a friend leads to unsafe driving behavior. A new study inspired by a court case involving a driver seriously hurt in an accident when following another car to a destination, provides evidence to show that the car behind makes risky driving maneuvers. Driving faster, more erratically, closer to the car in front and jumping traffic lights are all blamed on a fear of getting lost. Drivers are advised to provide the follower with a map or navigational guide before setting off. Source 9f.
I totally agree with the increased risk following people. The problem is that most people driving with someone following act like they aren't being followed. When I have someone behind me if the light is about to change then I'll stop. Some people will go through on a yellow knowing that there is a car following. Also, don't wait until the last second to make a lane change for a turn. That's always nice to deal with while following. .