A wastegate blanket works in a very similar way to a Turbo Jacket. After all, they experience similar conditions as turbos. External wastegates can get really hot as well, and the PHR blanket was designed to minimize the heat transfer between the main body and actuator body of the wastegate.
This will help alleviate wastegate diaphragm stress while in use, especially under extreme heat. The hot surface area can cause wastegate issues or boost creep. A better protected wastegate can ensure a more consistent performance, and a longer lifespan of your turbo.