Heredoc's are a great alternative to quoted strings because of increased readability and maintainability. You don't have to escape quotes and (good) IDEs or text editors will use the proper syntax highlighting.
A very common example: echoing out HTML from within PHP:
$html = <<<HTML
<div class='something'>
<ul class='mylist'>
<li>$something</li>
<li>$whatever</li>
<li>$testing123</li>
</ul>
</div>
HTML;
// Sometime later
echo $html;
It is easy to read and easy to maintain.
The alternative is echoing quoted strings, which end up containing escaped quotes and IDEs aren't going to highlight the syntax for that language, which leads to poor readability and more difficulty in maintenance.
Updated answer for Your Common Sense
Of course you wouldn't want to see an SQL query highlighted as HTML. To use other languages, simply change the language in the syntax:
$sql = <<<SQL
SELECT * FROM table
SQL;
First of all, all the reasons are subjective. It's more like a matter of taste rather than a reason.
Personally, I find heredoc quite useless and use it occasionally, most of the time when I need to get some HTML into a variable and don't want to bother with output buffering, to form an HTML email message for example.
Formatting doesn't fit general indentation rules, but I don't think it's a big deal.
//some code at it's proper level
$this->body = <<<HERE
heredoc text sticks to the left border
but it seems OK to me.
HERE;
$this->title = "Feedback";
//and so on
As for the examples in the accepted answer, it is merely cheating.
String examples, in fact, being more concise if one won't cheat on them
$sql = "SELECT * FROM $tablename
WHERE id in [$order_ids_list]
AND product_name = 'widgets'";
$x = 'The point of the "argument" was to illustrate the use of here documents';
Some IDEs highlight the code in heredoc strings automatically - which makes using heredoc for XML or HTML visually appealing.
I personally like it for longer parts of i.e. XML since I don't have to care about quoting quote characters and can simply paste the XML.
I don't know if I would say heredoc is laziness. One can say that doing anything is laziness, as there are always more cumbersome ways to do anything.
For example, in certain situations you may want to output text, with embedded variables without having to fetch from a file and run a template replace. Heredoc allows you to forgo having to escape quotes, so the text you see is the text you output. Clearly there are some negatives, for example, you can't indent your heredoc, and that can get frustrating in certain situation, especially if your a stickler for unified syntax, which I am.
Source: Stackoverflow.com