Not to be confused with actual holograms, aka projections.
Holograms are what helps you make your factories - they are what you see when you use your buildgun.
Circuitry has custom holograms with configurable settings.

Circuitry holograms allow you to pick the size of a grid that they will snap to, allowing you to create neat circuits instead of making a mess all over the place.
The size can be configured by going to pause menu -> Mods -> Circuitry -> Grid size
By default that value is 0, meaning the gate will be placed exactly where you're aiming.
Recommended values for gates are powers of 2, i.e. 2, 4, 8, 16, 32

Tip

The best grid size is (objectively) 8
Since we're in 3D space, larger values might snap your gate into a wall or where you can't interact with it.

In 0.12.20 update, the gates got the ability to snap to each other without using the grid settings.
Placing a gate and then trying to place one right next to it will cause the hologram to attach to the first gate, making a noise to indicate that it got snapped in place.

This behavior is also present in other objects such as screens, pixels, and lightbulbs.