The colon syntax can be useful when in project views/partials where you are mixing html and php. Below are some examples for quick reference.
<?php if ($a == 5): ?> A is equal to 5 <?php elseif ($a == 6): ?> A is equal to 6 <?php endif; ?>
<?php while ($i <= 10): ?> <tr> <td><?php print $i; $i++ ?></td> </tr> <?php endwhile; ?>
The following will create 10 table cells numbered 1 to 10.
<?php for ($i=1; $i<=10; $i++): ?> <tr> <td><?= $i; ?></td> </tr> <?php endfor; ?>
You can use colon syntax with switch statements but you (or someone else) are likely to break it later, accidentally with whitespace, so I'm not putting an example here.