I like your "period" analogy! Worth noting that you can put double-bars all over the place but, unless accompanied by a Rehearsal letter, the player will ignore it. I always use the left-side single bar, since the Editor automatically adds the bar at the end of a line when you start a new one below it. (Things get tricky when using Vertical-Space Arrows, but that's a different topic.) If you start a new line with a double-bar, the Editor leaves the end of the preceding line blank, reminding you to insert a double-bar (or repeat) there too. Scoring is usually easier when you let the Editor's logic help you along.