Cold brewing has some disadvantages compared to hot steeping. Firstly, if the leaves or source water contain unwanted bacteria, they may flourish, whereas using hot water has the benefit of killing most bacteria. This is less of a concern in modern times and developed regions. Secondly, cold brewing may allow for less caffeine to be extracted, which may or may not be desired.
Sun Tea is made by steeping the tea leaves in a jar of unheated tap water left in the sun. It does not get hot enough to kill bacteria present on the tea leaves or in the water.