Having duplicate contact records is obviously a problem. You may send multiple copies of the same message to a contact, which looks unprofessional; or you may look at a record and not be getting the entire picture because part of the contact’s data is attached to a duplicate record. By using CiviCRM's sophisticated "deduping" functions and instituting a little organizational discipline around your procedures, you can minimize duplicate contacts, learn where they happen and why, and avoid the issues they cause.
Go to https://greenleafadvancement.com/training to register.
CiviLunches are free one hour webinars brought to you by Greenleaf Advancement. Depending on the day they begin at either 12 PM Eastern US, 12 PM Central, or 12 PM Mountain (hence the name CiviLunch).