Confessing sin has been part and parcel of the Christian faith since the beginning. We know it's biblical- John the Apostle wrote, "If we confess our sins, he is faithful and just and will forgive our sins and purify us from all unrighteousness" (1 John 1:9 NIV).
In this passage, John doesn't specify to whom we should be confessing our sins. The context implies that confession of sin should be directed both toward God and others (See 1 John 1:7).
I suggest that we confess our sin to three parties: to God (of course!), to a more mature believer and to the person we have sinned against (unless to do so would cause them undue harm. This can be discerned with the help of a more mature believer). In James 5:16 we are encouraged to confess our sin to others.
Confession is important because when I "own" my sin, it begins to lose its grip on me. When I keep it in the dark, its roots grow deep and its power increases. Confession opens the door of our hearts to Christ's emancipating light. Saying, "I was wrong, please forgive me," to the person I have injured invites soul-liberation and relational harmony.
Confessing is hard. It requires that I admit I blew it. It's hard enough confessing my rude tone of voice to God. Confessing it to my wife who has been injured by it is harder, but doing so makes a way for me to be less rude and to bring healing to my wife's wounded heart. Confessing to a mature believer can also invite insight into why we are beset by particular sins and will help us see the relational nature of sanctification.
Ask the Holy Spirit to help you waste no time in confessing your sins to all essential parties.