To limit the probability of inadequate bridging of subfloor joints, which could lead to differential movement between adjoining subfloor panels, which could lead to the displacement or cracking of ceramic tile.
Where finished flooring is required to provide water resistance, this is to limit the probability of the ingress of water into the subfloor, which could lead to:
This is to limit the probability of negative effects on the air quality of indoor spaces, which could lead to harm to persons.