In what situations would it be necessary to normalize a table structure in PHP to optimize queries involving conditional INSERT commands?

```php
// Example of normalizing table structure to optimize queries involving conditional INSERT commands

// Original table structure
CREATE TABLE users (
    id INT PRIMARY KEY,
    username VARCHAR(50),
    email VARCHAR(50),
    status INT
);

// Normalized table structure
CREATE TABLE users (
    id INT PRIMARY KEY,
    username VARCHAR(50),
    email_id INT,
    status_id INT
);

CREATE TABLE emails (
    id INT PRIMARY KEY,
    email VARCHAR(50)
);

CREATE TABLE statuses (
    id INT PRIMARY KEY,
    status VARCHAR(50)
);

// Sample PHP code for conditional INSERT command
$username = "john_doe";
$email = "john.doe@example.com";
$status = "active";

// Check if email exists in the emails table
$emailExists = $pdo->prepare("SELECT id FROM emails WHERE email = :email");
$emailExists->execute(array(':email' => $email));

if ($emailExists->rowCount() > 0) {
    $emailId = $emailExists->fetchColumn();
} else {
    $insertEmail = $pdo->prepare("INSERT INTO emails (email) VALUES (:email)");
    $insertEmail->execute(array(':email' => $email));
    $emailId = $pdo->lastInsertId();
}

// Check if status exists in the statuses table
$statusExists = $pdo->prepare("SELECT id FROM statuses WHERE status = :status");
$statusExists->execute(array(':status' => $status));

if ($statusExists->rowCount() > 0) {
    $statusId = $statusExists->fetchColumn();
} else {
    $insertStatus = $pdo->prepare("INSERT INTO statuses (status) VALUES (:status)");
    $insertStatus->execute(array(':status' => $status));
    $statusId = $pdo->lastInsertId();
}

// Insert user data into the users table with normalized references
$insertUser = $pdo->prepare("INSERT INTO users (username, email_id, status_id) VALUES (:username, :email_id, :status_id)");
$insertUser->execute(array(':username' => $username,