I have my holy cards and rosaries blessed. When a priest blesses a holy card or rosary or medal, etc., he is praying God, on behalf of the Church, to bless the person who uses it. Because of this prayer, the devout use of these blessed objects brings various benefits, including: temporal favors (to the extent God wills them); the remission of venial sins and the punishment due to them; and protection from demons. I personally have blessed objects all over my house, in my car, in my office and on my person, and I keep supplies of holy water at home and in the office. I think we ought to make not only devout but liberal use of sacramentals, since this is what they are given to us for.
Incidentally, that God uses objects to dispense graces is well-attested in Scripture. Consider, for example, the bronze snake on the pole that God used to cure the Israelites of snakebites (Numbers 21); Jesus making clay and using it to cure a man of blindness (John 9); the use of handkerchiefs and aprons that had been in contact with the Apostle Paul to cure diseases and drive away demons (Acts 19).
