The oil life monitor uses a variable of monitoring cold starts, viscosity and other things. That is a golden question, but the answer is quite simple, and actually you can hold the owners manual accountable and correct. Older cars needed to have oil changes every 3K miles, the ecotec allows you to get the full life of your oil by monitoring it and alerts you to tell you when it determines the oil usefulness is gone. However, there are many factors involved such as driving and environmental conditions which may call for you to keep the 3K regimen, such as driving in extreme heat, heavy traffic or dirt roads.
When you press the toggle button on the DIC console to reset the trip computer, it will toggle between "OIL LIFE" and the trip mileage. Depending on how many times you pressed the button it may stay on "OIL LIFE", just press the button again to show your mileage. What the usefulness of this feature is, nobody knows.