Communal Penance Services are optional. I think it was instituted after Vatican II to encourage people to confess before the 2 major feasts of the Church (ie- Christmas and Easter) since regular confession has fallen off.
It has a parallel in the Jewish Day of Atonement in which the worshippers would all gather at the Temple. At one part of the ceremony, all the worshippers would stand, beating their breasts and, saying aloud all their transgressions for the year. Afterwards, the priest would sprinkle them with the blood of the sacrifice, ritually cleansing them from their sins. (source - working from memory - from ‘This is My God’ by Hermann Wouk - an excellent read for anyone wanting to know more about Jewish practices, past and present)
Our practice here for a communal reconciliation service is to have the first part ie - the Homily and an Examination of Conscience then our 3 priests (and sometimes a visiting priest) will each take a seat in secluded parts of the church, not in the confessionals but visible. Each of us, individually, make our way to the priest, confess and receive absolution. After confessing, we are asked to remain in the church until everyone who wishes has confessed . The service is concluded with a blessing. It generally takes about an hour to an hour and a half, depending on how many people come and how many priests we have available.
The time after confessing, while waiting for others to have their turn, can be used to say your penance or just to pray before the Blessed Sacrament. It is a very reverent service.
In some ways, I find this service more humbling than regular confession because you are there confessing in front of everyone and although they cannot hear you, everyone knows that you are owning up to your sinfulness.
There is no General Absolution, this being seen as inferior since you still need to confess individually anyway. We tried it one year but I think everyone, priests included, found it unsatisfactory. As far as I can see, it has the same effect as the general absolution at the beginning of Mass - which is to say, it is alright for venial sins but serious sins must still be confessed. Why bother going to a separate service then, when you will receive the same thing at Mass? I see a danger in it, in that some people might think that it has taken the place of individual confession and believe that they have fulfilled that requirement - especially those who haven’t been to Mass for a while.