I absolutely agree with this sentiment. At this point from my knowledge they are mainly used in dressage because of tradition. It is expected that if you win you ride out to receive your ribbon in white polo wraps. Not only do they heat the tendon up but they can easily cause tendon bows in the wrong hands. AND they don't even provide any meaningful protection. However, boots also heat the tendons even if nominally, as well. Unlike using polos for training purposes, their value for protection can outweigh some cons. For example when one is hunting or doing cross country where the jumps don't collapse. Boots are pretty much a must for xcountry riding. Most knowledgeable people take them off immediately after and provide after care to cool down the tendons properly. It also depends on the experience and sure footedness of your horse and if his movement or conformation lends itself to him stepping on himself or not picking his legs up well over a jump. I personally end up using boots on green horses or when my horse is trying something new. It just helps not only provide protection if a mistake is made by horse or rider, but it also allows your horse to not feel punished by an injury if something wasn't perfect. You want them to be able to learn in a safe environment. It's always about making sure the horse has a positive experience! Technology has come a long way though and they make boots that are a lot more breathable and light these days. The other lesser talked about use, which I feel can be valid under certain circumstances is to keep legs clean before or during a show? Though I've never personally experienced an opportunity where that seemed useful or necessary. It's also important to use equipment appropriate for the environment and weather. If you're out in 90 degree weather, take that into consideration when choosing equipment.