Breathing training (and other forms of meditation) can be an extremely powerful tool to increase the awareness of thoughts that promote chronic stress (or promote calm). Breathing training also increases the effectiveness for us to relax (or shed the stress response) on command.
Working with your breath this way can help you free your body of tension. Many of us are unaware of the tensions that are with us 24/7. Our breathing is designed to help us release any tensions that have become so much a part of us that we no longer sense their presence.
To understand how pausing works, consider that chronic stress affects the brain much as running too many applications simultaneously impacts your computer's performance. After all, the brain is a computer of sorts. And both suffer when overloaded.