Getting your Bearded Dragon substrate just right is one of the most important, controversial and hotly debated topics in the reptile keeping world.
The main controversy lies in the problems caused by impaction. Bearded Dragons are technically savanna/scrubland reptiles, and therefore exist in nature on loose dirt/sand; however, they can be messy feeders, sometimes ingesting small quantities of loose substrate in a hungry frenzy. Although impaction is a potential threat, with the right husbandry and temperatures, small levels of substrate ingested will pass straight through. Impaction really becomes a problem if the environment is not correct, so be sure to check temperatures regularly.
Many keepers use a sand substrate for Dragons, giving them a more natural enclosure that they'll feel at home in, though there are many other options, including carpets and mats that have no loose particles, reducing all risk.