I believe confessing venial sins is important, although not required. Confession helps us to reconcile with our Father, and what Didi wrote about it is particularly beautiful.
I had one experience of God’s grace - I don’t know what type as there are different graces God bestows, through the sacrament of confession. I left the confessional and felt this warm aura of love envelop me for weeks. Nothing could bother me, nothing could affect me. Suddenly I realized how much confession is a sacrament of love, not just absolution for our sins. Sin, all sin, inluding venial turns us away from the Father. Like the prodigal son, we have to return and renew our loving bond, so we can have a beautiful relationship once again. I also believe through confession we receive strength to resist sin and keep ourselves turned toward the Father. The Pope attends confession once a week. Saints, like Saint Augustine would attend often as well. My guess is that they didn’t have numerous mortal sins, but most likely venial ones.
My most recent penances have not been penances of prayer, but of charity - and as tough sometimes as that is to perform, I believe it’s been a wonderful lesson in my holy education.