The two biggest points of the template would be the tools that tell you how far your spacing should be.
1.Smoke detector placement tool : I have it in my tools as "Radius of coverage" This tool shows you the area of coverage of your smoke detectors. It shows you what 21 feet from the center looks like. What 15 feet to the sidewall looks like and 900 square feet of coverage looks like. You can also click a drop down menu to see the .7 rule of coverage for corridors.
As seen in this video
2. is the visual notification measurement tool: Some call it the strobe coverage template. This tool allows you to select the ceiling height from 10 to 20 to 30 feet to see what type of candela is required to cover a room.