Differences between tableView.dequeueReusableCell and UITableViewCell

Good evening,

I would like to know what is the difference between the parameters below, if one is more effective than the other, less chance of error etc. What I see in practice both do the same thing. Thanks in advance.

1)

override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {

   let cell = tableView.dequeueReusableCell(withIdentifier:"cellName”, for: indexPath) 
}

2)

override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {

    let cell = UITableViewCell(style: UITableViewCellStyle.default, reuseIdentifier: "cellName") 
}