Utilizing the custom spacer allows for exact mount placement when installing various array sizes. I always work from the lower left corner for small arrays such as a 3 by 3, but for 10 units wide it is best to start in the middle and work your way outward to account for any accumulating tolerance issues on the wall. Install the 1st mount, make sure it is perfectly level (laser level is best), then using 1 spacer, install the next mount always ensuring that each mount is level. As you progress horizontally and vertically, relocate your spacer to each new mount for exact mount location. Spacers are indeed a little pricy, we build them to order because not all installers want to use them, but, when you consider an investment of a $150 tool decreases a typical installation cost by reducing expensive labor, the $150 tool becomes a money saver because you don't have to layout the entire wall and position the mounts......the spacer does it for you. It pays for itself by the 3rd mount.