I've nearly finished my lambda service for my smart home skill, and everything works great. The Echo is receiving my confirmations and correctly relaying their information. I'm now trying to build in error handling.
From the SHS API reference, there are a bunch of error messages listed that correspond to different circumstances. Are these errors supposed to change what Alexa says? Regardless of which one, if any, that I use Alexa just responds that the command doesn't work on that device. Right now I'm literally just using callback(err) and return the copy and pasted object from the API reference and still Alexa responds with the generic error.
It's easy to put in a bunch of constants to define error returns. It's harder to wire all of that into a firmware patch of a hardware device. Also, they only release an update to the SDK a few times a year. While they patch the hardware every couple of weeks.
Given that, I suspect that they put those error returns into the SDK to meet with a ship date with the SDK. More as placeholders than specific functionality. Over time, and if there is increased adoption of home skills, they will roll out updates to the hardware device that will take advantage of those returns.
My advice would be to use them. But not to expect there to be a difference right now. And don't mention differences in your documentation. If there is another place you can surface diagnostic information, you might want to do that so your customers can fix their problems.