For example, both vim and emacs have snippet or template plugins (ex: yastnippet, snipmate, ultisnips, xptemplate, etc) that can be activated with a short keystroke and which then expand to whatever code or text the user desires. Then, depending on the features of the snippet/templating plugin in question lots of other advanced behavior (such as selecting items from a menu, activating sub-snippets/sub-templates, etc) can be activated. No need to use a steno keyboard for any of this.
Weirdly, though developed for Georgi the lightweight springs have found themselves back into Gergo and GergoPlex as users have reported it helping with their RSI flareups (compared to traditional mechs)
I used that for a couple common symbols in LaTeX' math mode, e.g. entering ;lra gets me a \leftrightarrow.
But I wouldn't recommend that approach for multi-line snippets and more complex cases, the config will get unreadable otherwise.