This can be used to change how often the preview window updates with a new image. Some digitizers have a software-based exposure level that compensates for changes in light conditions.
Many video cameras have auto-iris control.
If your camera compensates for brightness, leave the refresh rate. Because if the light level changes, the next time the video digitizer takes a picture, the brightness level will be incorrect. This can affect the quality of saved images, as well as cause the first few streamed images to be either too bright or too dark.