A general confession can be useful as one begins a new phase of life, for example, marriage, ordination, religious vows, Confirmation, or even as one begins taking the faith seriously for the first time, or a retreat. It can cover all or part of one’s life.
I have made general confessions on my yearly retreats that cover the previous year. It’s helpful to see the patterns of sin and to receive additional grace to continue fighting those sins.
A general confession is necessary in the case of a person’s having made a bad confession (deliberately hiding one’s mortal sins); it must cover the time since the last good confession, whenever that was.
To clear up a potential misunderstanding … One can always submit a sin to absolution, whether or not it has been absolved before. In order for the Sacrament of Penance to be valid, there must be actual sins confessed. If the penitent is making a devotional confession and does not recall any real sins since the last confession, he may renew his sorrow for a sin previously confessed and absolved. This gives the absolution something to work on and makes the Sacrament valid. This also gives an extra “shot” of grace to continue fighting against this sin. As stated above, this can also apply to a general confession.
Many people who tend toward scrupulosity are counseled NOT to revisit old sins, and this is excellent advice. It’s also a bad idea for people who cannot accept God’s forgiveness. But for regular folks with normal, healthy consciences, it’s perfectly fine to renew one’s sorrow for old sins.
Betsy