The Blessed Mother told Lucia, the oldest Fatima visionary:

"Look, my daughter, at my heart, surrounded with thorns with which ungrateful men pierce it at every moment by their blasphemies and ingratitude. You at least try to console me and say that I promise to assist at the hour of death, with the graces necessary for salvation, all those who, on the first Saturday of five consecutive months, shall confess, receive Holy Communion, recite five decades of the Rosary, and keep me company for fifteen minutes while meditating on fifteen mysteries of the Rosary, with the intention of making reparation to me."

The First Saturday Devotion

Does this mean people who do this can commit lots of sins? Of course not. All it means is that you will definitely die in a state of grace.  I believe if God knew you were going to commit a huge sin tomorrow, he would see to it that you died today.