It's as useful as you make it, for example if you have a URL, say your Facebook profile, and don't want your parents to know but still want to share it, you could write it out and share it. It requires the other person being able to understand how to use the tools required to type it.

It get's untypeable when it gets into the Kanji, so something like ㋖ュ isn't really untypeable but it will take you a bit.