When we go to Holy Confession, the priest reads a prayer before he begins listening to our confessions. In this prayer he states that we should not be ashamed before him to admit our wrongs, because he is only present as a witness, and in fact you are confessing to Christ Himself. He also says that knowing a sin and not confessing it compounds that sin...and he warns us that having come to the "doctor" we be weary that we get healed and not make ourselves even "sicker". Of course I paraphrased, as I don't know the exact words...but, this was the meaning.
I have always understood that the priest is present not to forgive. He doesn't have that right or capacity. Who forgives is God, alone. The priest is there as your shepherd. He is there to listen and when he realizes that one of his flock is having issues, he is there to offer advice, in order to assist them in their healing. He is there to hear our sins...and to pray for us. He is there to help us, not to forgive us.
When we complete our Confession, the priest does not tell you "you are forgiven", or your sins are "erased". He prays that God should forgive us our trespasses. He prays for our healing.
If we go away with a warped sense of being "cleansed" with the notion of repeating it again this week, because I can go get "cleansed" again next Sunday...we are sadly mistaken. Christ said "go and sin no more." ...and while we are not perfect....and we WILL sin again....we need to leave with the wholehearted intent of NOT sinning again. We need to fight against sin. We need to make a decent effort!
As for petty sins. First, there is no petty sin. If we don't recognize even our smallest sins...we stand the chance of not seeing our bigger sins. The more you "allow" yourself....the easier it will be to "allow" even greater sins. We need to make a conscious effort against all manner of sin.
However, as to confessing each and every thing....I believe the priest may frown upon that...as almost being self righteous, in a sense. If you've cursed out your coworker...and later you yelled at the bank teller for being slow....and then you got upset at your neighbor for something...and at your kids for disturbing you ...you don't need to tell the priest all the details, just say that you lost your patience and said unnecessary things. With the one statement you have mentioned them all. However, in YOUR heart....you need to remember ALL of them....and be remorseful....and try not to lose your temper again.
Just my opinion.