This stems from an encounter tonight while driving, but I've encountered it on my bike as well so I'm sure the car-free might relate.
Don't yield if you're not required to and it's not a helpful gesture. When I'm coming off an off ramp on a highway and see you coming, I'll slow down and stop. Sure, proceed careful in case I'm one of those idiot drivers, but don't stop completely as I come to a stop and pause before flashing your lights at me to say I can go. I'll wave and be thankful, but it wastes both of our time as we figure out who should go and both of our gas as we stop and start instead of slowly merging. If there's a long line of cars behind you, then sure be a kind soul and I'll be much more grateful, but if you're alone just don't.
Don't yield if I have a stop sign and there's only a few cars behind you. It will take far less time for all of them to pass and then me to continue than to wait until I understand that you'll let me go, especially since I can't see your brake lights. Again if there's a lot of traffic, I wouldn't mind being let out.
Same if I'm on a bike. If I'm waiting at a stop sign and you approach alone, don't come to a stop so I can see you'll let me go. By the time I see you're going to let me out, you could've passed if you didn't slow to a stop and I could be on my way. I understand you're being nice and I wish more people were like it, but you're going to have to pass me right after I get going and it will be more hassle for you than it would have been and more concern for me.
So it's good to know that there are still people in the world that pay attention and respect other drivers/cyclists, but help us out if it really will help us and not just lead to a moment of confusion, which can become dangerous.