Benefits of "Behind the Screen” Confession
1) Easier to recollect sins because of the absence of having the priest looking at you while you are trying to do it, thus rendering confession more thorough and thus more fruitful. When going to confession it is hard enough to confess embarrassing sins to another person, but becomes all the more embarrassing when you have to tell these sins while being looked at.
2) Preserves anonymity and allows the penitent to be freer in confessing his sins. When the priest knows the person, the penitent may feel judged or think that the priest will remember the embarrassing sin. The anonymity also, in a way, symbolizes the gratuitous nature of God's grace, who gives without distinction of persons. The fact that the priest cannot see you is in a way symbolic of the fact that to God all men are equal and that He judges by the heart.
3) Justice. When the priest does not know who is confessing, he is freed from human respect and can be a direct to the penitents about the seriousness of their sin. It is only just to tell all penitents the same truth and the same correction. But if the priest knows the one who is confessing, he might be afraid to be direct because we all tend to want to be liked.
4) Keeps confessions shorter; it is harder to get into a "discussion" from behind a screen.
5) Sign value: placing yourself behind a screen with the priest, acting in persona Christi, reminds us that sin does indeed put up a barrier between ourselves and God.
6) Greater humility: when we are visible to another person, especially a priest, we will tend to try to look more impressive in our demeanor and facial expressions. Behind a screen (especially if there is a kneeler), we are enabled to forget our image and truly humble ourselves. This is the proper disposition for the sacrament and thus makes it more fruitful.
Disadvantages of "Face to Face" Confession
1) The biggest and most obvious one is lack of anonymity. Confession of sin, since the early Middle Ages, has always been anonymous (in patristic times, it had been public, before the congregation, which I don't think anybody is anxious to return to). Knowing that the priest is now able to connect a face with the sins you are confessing makes it more difficult to bring everything out into the open.
2) It creates the atmosphere of a meeting room or a psychiatrist's office. A face to face format encourages discussion; after all, in society, we are always face to face when we discuss things. Thus, from habit, we tend more to want to "discuss" our sins instead of confess them. Behind the screen, it is easy to say, "Bless me Father, for I have sinned. It has been six weeks since my last confession. I confess that I have..." It is awkward to repeat this formula while you are sitting face to face with the priest. Instead, the confession tends to sound like, "Oh Father. I'm having such a problem with my daughter! Let me tell you about it..." This is one of the biggest problems of face to face confession; instead of confession of sin, it turns into discussion of problems.
3) Flowing from the above tendency of confession to turn to discussion comes the consequent that confessions take a lot longer; it takes a lot longer to discuss things with a priest face to face than to simply make a confession behind a screen. Face to face confessions often run twenty-minutes a piece. The average confession made to St. Padre Pio was under two minutes.
4) It fails to give any sense of the fact that sin puts you outside of God's grace; i.e, the sacrament done face to face has very little sign value. It has the feeling of a fireside chat.
Now, there might be some good reasons why a penitent would prefer “face to face” Confession, such as a person in a motorized chair or someone who is hard of hearing and greatly aided by lip reading. In such cases, just approach the priest and make a special arrangement for “face to face” Confession somewhere in the church before or after Mass, or at the parish office during office hours.
In conclusion, Confession “behind the screen” has several advantages: helps instill greater humility, makes it easier for the penitent to recall his sins, preserves anonymity, keeps the confession time shorter (making it more practical) and, if the proper dispositions are all there, facilitates a greater reception of grace ex opere operantis to the penitent.