UTF-8 is a stateless encoding, i.e. a self-terminating short byte sequence determines completely which character is meant, independent of any switching state. G0 and G1 in ISO 10646-1 are those of ISO 8859-1, and G2/G3 do not exist in ISO 10646, because every character has a fixed position and no switching takes place. With UTF-8, it is not possible that your terminal remains switched to strange graphics-character mode after you accidentally dumped a binary file to it. This makes a terminal in UTF-8 mode much more robust than with ISO 2022 and it is therefore useful to have a way of locking a terminal into UTF-8 mode such that it can't accidentally go back to the ISO 2022 world.
I had noticed that I hadn't gone cyrillic since I moved to OS X almost two years ago. UTF-8 is the default encoding for my Terminal on OS X but I never made the connection. This used to be a real problem for me as a kid when my friend Ray's System V.4 machine spent a fair amount of time at my house. I was young and stupid and would accidentally cat binaries to my terminal, leaving it in a completely unusable state. For some reason, there was no /bin/reset on that particular SysV machine and I was unable to logout so I would have to unplug the terminal from the rs232 port in the back and plug it into one of the unused ones farther down so I could login again. Once in a while, I'd forget that I'd used up all 16 of the tty's on the machine and would be out of available terminals. At that dreaded moment, I'd have to reboot the machine.
You really don't want to reboot a 1980's-era Unix mini without properly shutting down...
... So, after reinstalling the operating system from tape and praying that my latest backups (if I had bothered) were good, I'd go on for another few weeks accidentally catting binaries like a fool until I ran out of tty's again, playing Serial Port Leapfrog along the way, reinstalling my OS every few months or so. After all that, you'd think that I would've written my own 'cat' wrapper that would check the magic number to make sure only text files were catted out. You'd think.
Life's a lot better with Unicode.
# — 13 November, 2003