Certain simple kinds of changes don't need much detail in the change log.
When you change the calling sequence of a function in a simple fashion, and you change all the callers of the function to use the new calling sequence, there is no need to make individual entries for all the callers that you changed. Just write in the entry for the function being called, “All callers changed”—like this:
* keyboard.c (Fcommand_execute): New arg SPECIAL.
All callers changed.
When you change just comments or doc strings, it is enough to write an entry for the file, without mentioning the functions. Just “Doc fixes” is enough for the change log.
There's no technical need to make change log entries for documentation files. This is because documentation is not susceptible to bugs that are hard to fix. Documentation does not consist of parts that must interact in a precisely engineered fashion. To correct an error, you need not know the history of the erroneous passage; it is enough to compare what the documentation says with the way the program actually works.
However, you should keep change logs for documentation files when the project gets copyright assignments from its contributors, so as to make the records of authorship more accurate.