On an unshaded flat roof in Dubai we routinely measure surface temperatures above 75°C in August. A correctly applied reflective coating brings that down to the mid-40s.
The benefit is twofold: reduced cooling load, and dramatically slower thermal ageing of the waterproofing beneath.
The caveat is preparation. A reflective coating applied over a dirty, unprimed or already-failing membrane will delaminate within a year and provides no measurable benefit.
Reflectance also degrades with dust accumulation, which in the UAE is significant. A washdown twice a year recovers most of the lost performance.