As was mentioned earlier, there are some roaster ovens that are equipped with a Keep Warm setting. But, it was not discussed in-depth and there have actually been users across the web who have asked this question. Now, to some people, it may seem like a rhetorical question and yes, it is wise not to overthink this one as the name of the setting does exactly what you would think it does. When you turn the knob on your roaster oven to Keep Warm, the roaster is going to stay warm enough to keep your food from cooling but cool enough to prevent it from cooking further.
Because it maintains a low heat, you do not need to worry about your contents inside burning; which is exactly why it is a handy feature. Otherwise, leaving your food inside could lead it to become overcooked and no one wants that.