The Church requests that all Catholics attend confession at least once a year, although it prefers at least twice. While it would be best to continually unburden ourselves as the year goes on, it is especially good to do so before the major celebrations of Christmas and Easter. This way, when we partake of the Eucharist on these most holy days, we become one with Christ as we remember His birth and rebirth without any shadow haunting the joining.
We humans are not a perfect species even if we were created in the image of perfection. Despite the amazing miracle of our creation, we are hampered by our sinful nature. I know that it isn't politically correct to discuss our imperfection, but denying its existence does nothing other than to give it more power over us. Saying that we have no need for improvement stops us from growing into the best possible versions of ourselves. Acknowledging our faults allows us to overcome them.
God doesn't want our confessions so that we can beat ourselves in our guilt. He wants us to be part of His perfect love. One cannot strive for such a goal without knowing where one stands. Our self-examination and understanding of the difficult journey ahead of us lights a path for us to follow.
God already knows what we have done and not done. He simply challenges us to recognize the truths that we think we can hide from Him and ourselves, the flaws that keep us from perfection.