What exactly does physically based materials mean and what is the impact of this on your scene? Physically based materials mean that the material will actually react to light in the correct way and not how we intuitively think it should react. The end result is more accurate and typically looks more natural.
If you want to learn more about this subject, have a look at https://www.allegorithmic.com/pbr-guide.
Allegorithmic have created two guides for the theory and practical of physically based renderings.
Materials are an essential factor for producing believable renders and Lumion's team have done a great job by providing more than 600 materials that can serve as a base for your scene.