But the computer industry sure wants us to know and they want us to buy the latest and greatest software to prove it. Your first line of defense in avoiding trapping traps is to understand the concepts. This process has been around nearly as long as offset lithography. More so before the industry developed precision, high-tech printing presses. When printing color, a separate impression is required for each color.
Many variables can cause the two colors to be slightly misaligned or out of register.
This is usually not an issue because the human eye cannot perceive slight variations in positioning of objects. I was an apprentice in the camera department of a large printing company. Spreading made the positive image larger - spreading it into the background. The mylar caused the light in camera to refract at a slight angle, resulting in an enlarged image. Which film went on top determined choke or spread, and the thickness of the mylar determined how much image change would take place.