Well, for example a cross-guild tool, communication is forced to happen on chat channels... GuildAds is one such tool (but has its own encoding/decoding) and GuildEventManager as well.
Ideally, Blizzard should provide addon-channels on the same principle as normal chat channels. Maybe even just enable addon messages to happen on the chat channels you are on (except perhaps the general/trade/etc channels). But until this is possible, normal chat is the only way.
Anyway, addon channel allows every but \000. Chat channels is something like:
This can be done. Requires more than 1 escape character or deeper nesting. But doable.
Check out AceComm-2.0 's code wrt chat channel comms, it covers just about everything iirc.