The same mechanism can be used to type a long word with just a few characters. Especially useful for words which you find hard to type, and it avoids that you type them wrong. It is best to use short words which don't have an meaning of their own. To find errors in your text Vim has a clever highlighting mechanism. This was actually meant to be used to do syntax highlighting of programs, but it can catch and highlight errors as well.
Syntax highlighting shows comments in color.
That doesn't sound like an important feature, but once you start using it you will find that it helps a lot. Unbalanced braces can also be catched by the syntax highlighting. Any word not in this list could be an error. With a syntax file you can highlight all words that are not in the list. With a few extra macros you can add words to the wordlist, so that they are no longer flagged as an error.