I don't even need to prevent printing etc.
I'd also love a setting, email over 1 year old, you have to jump through some extra hoops to access it.
Only if you have complete end-to-end control over all the devices that everyone uses, including their brain, can you stop people from copying data.
If I have a file that I want to limit access to, I would never dream of sending it via e-mail. Some hosted document service which only shows parts of the file would be far preferable.
There are plenty of scenarios where the sender may be confident that the recipient will not intentionally betray their trust but may not want to leave long-term traces behind (say, forwarding confidential documents to a family member). Rather than reminding them not to forward the email and to delete it ASAP, you could just use this feature instead.
Just because something doesn't can't cover all scenarios doesn't mean it's useless. Firefox's Private Browsing can't hide your activity from a determined eavesdropper, for example, but there are still plenty of ways in which it's useful.