Very useful when creating entries from one date to another. The basic way would be the following:

$startDate = new \DateTime('2020-06-01');
$endDate = new \DateTime('2020-06-30');

for($date = $startDate; $date <= $endDate; $date->modify('+1 day')){
    echo $date->format(\DateTime::ATOM);
}

The one I prefer would be using a period:

$startDate = new \DateTime('2020-06-01');
$endDate = new \DateTime('2020-06-30');

$interval = \DateInterval::createFromDateString('1 day');
$period = new \DatePeriod($startDate, $interval, $endDate);

foreach ($period as $date) {
  echo $date->format(\DateTime::ATOM);
}