It has been convention to attach prefixes to the subject every time during an email conversation, leading to subjects like:

"Re: Fw: Re: Re: Re: Original Subject"

Since email clients have started to group conversations, these prefixes are not really helpful anymore. I often remove prefixes before I send a message. An option not to add them, or even better remove them, upon replying/forwarding would be nice.

(Removing might be difficult though since those stupid prefixes often differ by language)