Being in control on the fire ground is critical for the fire officer. Nothing is worse than an officer screaming and shouting about EVERYTHING!
This shows a lack of control on the part of the officer. Staying in control allows you to think more clear, instills confidence in your members and allows for members and other officers to actually understand what your saying over the radio or through your mask.
The more your scream and lose your cool, the more inept you appear.