Final answer:
If end-closures are not installed on a concrete tile roof, the most significant issue that can occur is water intrusion, leading to potential damage and leaks inside the building.
Step-by-step explanation:
If end-closures are not installed on a concrete tile roof, the most significant issue that can occur is water intrusion. Without proper end-closures, rainwater can seep into the roof, potentially causing damage to the structure and leading to leaks inside the building. This can result in costly repairs and compromised functionality of the roof.
On the other hand, the absence of end-closures does not have any positive impacts like improved ventilation, increased energy efficiency or enhanced aesthetics. End-closures primarily serve as a barrier to prevent water intrusion, ensuring the roof remains durable and resistant to leaks.