For me it all depends on the internal client. What works for one does not for another. I tend to start in Storyline so that I am not duplicating my effort. In one project, I worked in an iterative process. I met with the SME and we reviewed the overall concept. As I began to build out the course, he wanted it in a Word document. No problem. I used Storyline's Word output. I dropped in comments to clarity aspects that do not come across in a one dimensional way.
For another client, we met and discussed the content--in pieces because it was very complex. I figured out the type of interactions that would work and met again. I shared my screen with him and we reviewed what I created and then next I sent him a link via tempshare so he could play around.
This went on until we covered all the bases of what was needed.
Still another client needed a storyboard with all the audio written and potential images to use. I created a storyboard in Word before I opened Storyline.
So that is my 10 cents!