The drivers around you have an expectation that you are going to operate your vehicle in an orderly and predictable fashion which maintains the natural flow of traffic. Any time you yield your right of way, you not only introduce an unknown factor into the mix - the other driver who doesn't have the right of way, but your expected action deviates from the natural flow and another driver who may not be paying attention can get caught off guard resulting in an accident.
My father also taught me to never follow a driver who has damage to the rear end of his vehicle for, chances are he performs erratic and unexpected behaviors which can cause accidents with drivers behind him.
There is an old joke about an elderly driver who gets pulled over for doing 35 in a 55. She tells the officer that she has never had an accident in her life but a lot of drivers behind her have. That joke demonstrates that a driver who is driving in an unexpected fashion can interrupt the natural and expected flow of traffic.
Here is a short video demonstrating the dangers of being nice or, as my father put it, "driving someone elses car."
You can see me driving down the road while there is a line of stopped traffic on my left. A grey van is looking to get out of a parking lot and the driver of a black SUV decides to be nice and most likely waves him out - not taking into account that I am coming from the other direction. The driver in the grey van takes the word of the black SUV that it is safe to cut across when, it wasn't. You can see that she cuts right in front of me. Luckily I wasn't texting, eating, changing my clothes, putting on make up, talking on the phone or rifling through the glove box as I see so many other drivers do. Because I was paying attention I was able to brake in time. You can see that I also began to veer off the road a bit in anticipation of a crash.
Further analysis of the video will reveal that if the black SUV waited, there were not many vehicles behind them and the grey van could have navigated themselves out of the parking lot all by themselves in their own time.
The lessons here are (1) never tell someone else how to drive their car with a wave for, chances are you can't see what they see and you are only focused on being nice, not the ancillary drivers who don't know what you are doing with someone else's car. (2) Never take the word of a nice driver that it is safe for you to move because they can only yield their right of way, not that of ancillary drivers.
If someone waves for you to pull out and another car hits you, whose fault is it? The guy who hit you? You for cutting in front of them? Or the guy who told you it was safe to pull out?
Nice is different than good. Be a good driver, not a nice one.