Vin. Good question and why I hesitate to post much on these groups. I primarily prefer to work with students in person (groups or individually). It's just my personal preference. There is SO much to say and I don't have the time or patience to type a lengthy explanation that makes sense AND covers all the 'if, ands, and buts' that come up.
So to try and clarify: I am only talking about Juniperus chinensis itoigawa. I would not paint a broad brush to include all the various species of juniper.
Regarding your question on trimming runners. Yes, you do that - once you get the plant to a healthy state. The runners are a sign that it is growing strong and obtaining a healthy state. After this is achieved, when you are to start styling, refining, etc. you can then cut these back to create pads, depth, etc. I was only talking about runners at the stage of creating a healthy state for the tree. I hope this makes better sense.