There was a specific time in my life when I was heavily entrenched in a secret sinful relationship. I can say from experience that it is so harmful to your life with God and with other believers. The effect was definitely a severing of true fellowship. When this sin came to light and I was able to confess it publicly, while it was embarrasing and it hurt, the result was an amazing feeling of freedom and light and extreme gratefulness to God for forgiveness and cleansing.