MongoDB - Why should I use a cursor instead of iterator_to_array (in PHP)
Using iterator_to_array() makes your driver load all of the results into memory at once, and you could easily run out of memory. This would not be the case with a cursor, which uses lazy-loading!
Straight from the linked docs:
<?php$cursor = $collection->find();var_dump(iterator_to_array($cursor));?>...
Suppose that, in the example above,
$collectionwas a 50GB collection. We certainly wouldn't want to load that into memory all at once, which is what a cursor is for: allowing the client to access the collection in dribs and drabs.