Dangers of untreated laceration and infection?

Worse outcome. Lacerations may leave vital structures like tendons, vessels and nerves uncovered. More superficial lacerations may simply have a worse scar if allowed to heal by secondary intention. Surgical debridement and appropriate cleansing of the wound are also potentially necessary. Wound infection can lead to increased morbidity and e en death if left untreated.
Yes there are! The location, depth, contamination, and health status of the individual with the cut all play a role here. Not to mention the tetanus status. When in doubt, see a doctor, but you need to do so promptly, as delay can make a wound unsuitable for repair because of time-related bacterial contamination and increased risks of infection. Can't put the lid on the garbage can. Unrepaired also=worse scar!