Apart from shorn horses, old and sick animals will benefit from a stable rug. But a stable rug can also be useful for healthy horses if they are often exposed to draughts, are kept in an open stable or are transported in a trailer. A healthy horse that is not shorn will not be bothered by the cold alone. However, things become more problematic when humidity, wind or draught are added to the equation.
Not every stable rug is windproof or waterproof, but these features become essential as soon as your horse goes outdoors. You can put a stable rug on your horse as a liner under a waterproof rug. Then you have an ideal combination: the warmth of the liner, plus the waterproofing and windproofing of the waterproof rug.