It scalds the tea leaves and extracts compounds that make the tea bitter or destroys some of the more delicate flavours. The exact temperature depends on the tea. When I was buying Dragon Well tea (Longjing) in China they explained it very well, but even went so far as to say that many of the health benefits of tea (especially Dragon Well, but others as well) were reduced by using water that is too hot.
Personally I’ve found tea and coffee taste better when brewed with water that is under 90°C.
When I was a kid, my best friend and his siblings took in a “stray” cat and gave it some milk (because cats love milk in cartoons, right?). The cat proceeded to spray shit all over the house including on carpet. To clean it up before their parents got home and found out, they decided to use the vacuum cleaner.
The next time their mom went to use the vacuum it created an unholy stench that basically made the house unlivable for several days. 100 percent do not recommend.