Before: For example, a baptism can be done when the person is a baby or when they are old enough to make the decision for themselves.
After: For believer baptism, the theological thought behind this decision is allowing the person to actually make the decision to be a Christian when they understand the significance of that decision. With infant baptism, it is a promise to the church that the family will raise their child as a Christian. The church then promises to assist the family in raising the child and supporting the family.