Why should scuba tanks always maintain some pressure?

Maintaining some pressure in scuba tanks is crucial to prevent water from entering the tank. If a tank is completely empty, there is a risk that water could seep in if the tank is tilted or oriented incorrectly. The pressurized air inside helps create a barrier that keeps water out, ensuring that the internal components of the tank and the air supply remain uncontaminated and functional.

While the other options touch upon various aspects of scuba diving, they do not address the primary reason for maintaining pressure in tanks effectively. For instance, buoyancy is more related to the diver's equipment and body, corrosion can be mitigated through maintenance rather than merely pressure, and while performance can be influenced by the quality of equipment, it is not the main function of maintaining pressure in the tank itself. Therefore, keeping some pressure in scuba tanks is essential for protecting against water ingress.