you can also kill your plants with the cold. you want to ensure it does not go below 3 degrees C outside at night. if you live in a cold climate its best to "harden off" your plants, by slowly exposing them to the weather outside.Start by putting them in shaded area for a day or two, and let them get used to natural sunlight. Work your way up to direct sunlight for longer periods over a few days.
As to the importance, you can kill a plant right quick by simply moving it outside into direct sunlight. I know, because I've done it.