"As you well know, venerable brethren, it is true that venial sins may be expiated in many ways that are to be highly commended. But to ensure more rapid progress day by day in the path of virtue, we will that the pious practice of frequent confession, which was introduced into the Church by the inspiration of the Holy Spirit, should be earnestly advocated. By it genuine self-knowledge is increased, Christian humility grows, bad habits are corrected, spiritual neglect and tepidity are resisted, the conscience is purified, the will strengthened, a salutary self-control is attained, and grace is increased in virtue of the sacrament itself" (Mystici Corporis 88 1943, Pope Pius XII).
There is a huge misunderstanding which grew up in the 1970s, as to the need for confession regarding venial sins.
Venial sin weakens the will and opens one up to more temptation. Venial sins usually arise out of the predominant fault, which must be overcome in order to achieve perfection.
The Church is weakened as well by those who daily commit venial sins.
Frequent confession makes one aware of one's self, one's venial sins, and one's predominant faults.
To only go to confession when one commits a mortal sin is not a good habit.
Remember, self-knowledge is humility and humility is absolutely necessary for perfection.