Final answer:
Interlaced scanning in a TV monitor is primarily used to reduce unnecessary flicker by alternately scanning odd and even lines of the image.
Step-by-step explanation:
In a TV monitor, interlaced scanning is used primarily to reduce unnecessary flicker. This technique involves displaying the image on the screen by alternately scanning odd and even lines, hence refreshing the image in a way that minimizes the flicker sensation to the human eye. The other options provided, such as quantum mottle, distortion, and low brightness levels, are not directly related to the use of interlaced scanning in TV monitors.