For anyone else that comes across this, check out this nice blog by some guy named “Steve” 
For anyone else that finds this, a quick summary:
FDebugRenderSceneProxy is useful for rendering debug lines, cylinders, circles, etc in the editor, without needing to click the “play button”
I’ve made use of this to show the bounds of a simulated object or constraint (like a spring on a car) while configuring it in the details panel.
You can render debug lines in the viewport of a blueprint or in the main gameplay viewport.