Technically this is true. However, you do not want to go too low in volume as the lower you go the more signal you will lose in the inital export, which can ruin your track in the maximization stage in mastering. Generally -3db is the ideal level you want to export with the intention of having your track mastered; meaning that the volume of your track should not exceed -3db in volume. The empty space on top is called “headroom.”
If you are working with a good sound engineer they will adjust the volume during the mastering process to ensure you have enough headroom to master the track. We usually find ourselves adjusting tracks to anywhere from -5db to -6db peak volume for mastering. In other words, you want to export at the loudest possible volume to ensure you get all the signal through while still leaving enough headroom for the mastering process.