When trying to lay out multiple components for a single metric -- say a single number, a comparison, and a trend line, it can be hard to delineate which visualizations "go together." I've been known to drop a text visualization with a space in it as a clunky way to make a horizontal line. But, there's no option at all to put any vertical delineators.
Having "decoration" visualizations that enabled some level of visually grouping / delineating blocks of visualizations would be very useful when using Analysis Workspace to make a dashboard that is readily scannable by end users.