function checkApprovedStatusToNotify() {
  let sheet = SpreadsheetApp.getActiveSheet();
  let lastRow = sheet.getLastRow();
  let lastCol = sheet.getLastColumn();
  // lastCol here is the NOTIFIED column.
  let frozenRows = sheet.getFrozenRows();
  let beginningRow = frozenRows + 1;
  let numRows = lastRow - frozenRows;

  // Gets ranges of email, approval, and notified values for every employee.
  let emailValues = sheet.getRange(beginningRow, COLUMN_NUMBER.EMAIL, numRows, 1).getValues();
  let approvalValues = sheet.getRange(beginningRow, COLUMN_NUMBER.APPROVAL,
      lastRow - frozenRows, 1).getValues();
  let notifiedValues = sheet.getRange(beginningRow, COLUMN_NUMBER.NOTIFY, numRows,
      1).getValues();

  // Traverses through employee's row.
  for (let i = 0; i < numRows; i++) {
    // Do not notify twice.
    if (notifiedValues[i][0] == 'NOTIFIED') {
      continue;
    }
    let emailAddress = emailValues[i][0];
    let approvalValue = approvalValues[i][0];

    // Sends notifying emails & update status.
    if (approvalValue == 'IN PROGRESS') {
      continue;
    } else if (approvalValue == 'APPROVED') {
      MailApp.sendEmail(emailAddress, APPROVED_EMAIL_SUBJECT, APPROVED_EMAIL_MESSAGE);
      updateNotifiedStatus(sheet, notifiedValues, i, beginningRow);
    } else if (approvalValue == 'NOT APPROVED') {
      MailApp.sendEmail(emailAddress,REJECTED_EMAIL_SUBJECT, REJECTED_EMAIL_MESSAGE);
      updateNotifiedStatus(sheet, notifiedValues, i, beginningRow);
    }  
  }
}
Checks the approval status of every employee, and calls helper functions
to notify employees via email & update their notification status.