If you actually bother preemptively reading your software documentation, you may have already known this, but this is a huge time-saver over having to render test movies for my HDTV.

At work, I'm using a 27" 1080p monitor/television as my secondary monitor. We use a model that has a similar color profile for presentations, so using this screen as a preview screen is essential. Otherwise, we'd have to keep our presentation displays unpacked and hooked up to a computer, transfer files, and so on. I won't get into (more) details, but suffice to say it would be a royal pain.