Writing good log entries

If one can use cvs diff to retrieve the actual text of a change, why should one bother writing a log entry? Obviously, log entries can be shorter than a patch, and allow the reader to get a general understanding of the change without delving into its details.

However, a good log entry describes the reason the developer made the change. For example, a bad log entry might say, "Convert to lower-case." This would be accurate, but completely useless; cvs diff provides all the same information, more clearly. A better log entry would be, "Make this test case-insensitive," because it makes the purpose clear to anyone with a general understanding of the code: HTTP clients should ignore case differences when parsing reply headers.