You know how it is. You're stopped in traffic and look up to see a helpless motorist trying to turn, but they just can't see around you or the other cars. What do you do? Do you serve as their lookout and let them know when it is safe to pass, or do you let them fend for themselves. Because nobody likes bad driving karma and because there are still simply nice and helpful people in the world, many drivers decide to lend a helping eye and motion to the turning driver when it is safe to pass.
But this is one situation when you should not be the good guy.
As I demonstrate in the video, even though you may have a better vantage point than the turning driver, you do still have a blind spot and may not be able to fully see oncoming traffic. Not to mention, you cannot control what the turning driver assumes you mean with your waving gesture. If a turning driver causes an accident after your gesture indicating that it is safe for them to turn, you may be held partially at fault for that accident, even though you were just trying to help someone out.
You should also never rely on someone who might be generous enough to wave you through for all the same reasons. Additionally, you really do not know if that is what their gesture meant. It could be that they are in the middle of a phone conversation and what looks like a wave to you was simply a conversational habit. You might be pulling out into a very dangerous string of oncoming traffic that could be deadly for you or someone else.