Do you know when you should change an email/appointment subject?
Some email threads go on forever... sometimes the topic subtly changes... so when should you change the subject? The answer is "cautiously". The reason is email threading.
So when do you change it?
When the original email theme has been superceded by new content
You should change the email subject to a more relevant description of the content of the thread.
"Field of Study"
"Next Years Conference WAS: Field of Study"
If the original subject was too generic, like "Reminder" or "Invoice" (especially when automatically generated)
Change the subject by adding the client or project name to the email subject.
"Northwind invoice for website - March WAS: 'Invoice'"
Remember, never forget the importance of a good email subject in improving communications.