when doing fan balancing you have to get the "moment weight" of the blade correct. That is why when changing a damaged blade ( that is not the same moment weight) you often change opposing blade with one of the same moment weight. By doing this you dont need to do a fan rebalance.You do indeed remember correctly. The further from the hub the mass is the bigger effect it has on balancing. A small mass at the prop tip puts it out of balance as much as a much bigger mass near the hub.
for small nicks I would suggesst a minute drop of super glue to stop the crack propergating. IMO if there is a bit od unbalance it is not going to cause the drone to crash but most likely cause vibration which may affect the camera. Better still lash out on a new set.