Have the bulk of the information you want to cover? Perhaps you already have a brochure or website that tells the important parts of the story. Have the idea in your mind but not all of the details worked out yet? 
For every project you might still have known unknowns left to fill in. You might also have unknown unknowns.
Need a battle tested format to make sure you are on the right general points? Although this is covered less if you were to do online research than say, for example, how to format general points for a landing page, well - they end up being pretty similar (if not the same).

Perhaps you want to test out different versions and you don't quite know what your main condensed headline or tagline is yet. Motion Storyline offers you a "distraction free" mode copied to be as much like Wordpress as possible to let you create and write out the parts you want to start out with. Place in filler for the parts you don't quite have or add it in when you have finished the rest.

Motion Storyline is not a video editor, and will not produce a Hollywood inspired (in it's heyday... but I digress) world class advertisement - but it can serve both as a tool to visualize your messaging as well as create a simple social media promo video! Primarily message focused, the format tracks the same as landing page marketing format and is built around text. The format is flexible enough to allow for still images (if available) or pre-shot video. Add your own background music (optional) and record your voice as a voiceover (optional) - but keep in mind social media format can be silent-by-default, so projects stand on their own without sound. 

Just as you might not quite be done with all the copy or production for your video project (but you will soon!), please allow Motion Storyline a bit of room for improvement. It is not finished but is an ongoing endeavor, and can always use feedback - click the lower right button from the dashboards for your project!