Why some officers of swat wear masks and others don麓t?

i always see some officers of swat with and others without balaclavas, why some use and others don麓t?Why some officers of swat wear masks and others don麓t?
Some hide their faces for protection or to hide their identity for possible under-cover reasons or some type of retaliation against them or their families. Sometimes its just for protection from debris and things. Overall, you would probably have better luck asking this in the Law Enforcement section. Why some officers of swat wear masks and others don麓t?
Because some officers work undercover and don't want to be identified as police