I think if they pertain to the case they should be. If a person is part of a murder trial, and they have a history of violence, that information would help. I think to just ignore the past convictions would be silly, they need to be looked at in full view.
Yes, it helps in the sentencing process. If a person is a first time offender they should be given a lighter sentence (depending on the crime.) If a person is a habitual offender, most importantly in cases of violent crimes, the sentence should be more strict. If someone is a serial rapist, or pedophile, it should be known to reduce the chances they do it again.
Previous convictions should be disclosed in court because sometimes those convictions lead to more crimes in the future. Criminal prosecutors need to show the jury that someone is dangerous and needs to be in jail longer for committing more crimes. Stating someone's previous criminal record casts dispersions against the defendant's character.
Yes I think that previous convictions should be disclosed in a court of law because sometimes they prove a point in showing a pattern of behavior that the defendant has created. If someone has a series of violent crime convictions, I would be more likely to seek a more severe punishment.
If previous convictions are disclosed in courts, it could create a bias in the jury that is impossible to overcome. For example, if a convicted child sex offender shows up in court fighting a small drug charge, the jury might be bias against the defendant because they also want to punish child sex offenders. Therefore, previous convictions should not be disclosed in court.