Documentation of change is required after it is approved as people leave the project in the middle and it is necessary that the person replacing the one ho worked previously knows why exactly was the change made and will be easier for him/her to understand the project and no detail has been missed.
I think every change has to be important in a project as we cannot actually have a say which one is of higher to the other.
The PM has to look pass logging everything as this might be of some use in future for reference and it would be a waste of time and money if the same change is repeated again in some other project in future.