There is absolutely no reason to ever take your helmet off to make a call, due to the visibility of a helmet.
But...I take mine off in every situation I would take off a mask. Again, not because I need to, but as part of the "show" to keep the coaches, and Big "old" Dogs, happy.
Here is a link to my experience wearing a helmet for about 6 years now.
http://www.reegind.com/helmet.htm