php - Using an object as a parameter vs creating the object in the method -

during discussion, wasn't sure if correct when saying:

"it's better pass around objects parameters instead of object id's."

so thought i'd ask here clarification.

what advantages of doing this:

public function dosomething(\item $item)  {         return $item->getsomething() * 2; } 

over this:

public function dosomething($itemid)  {     $item = \item::getbyid($itemid); // return item based on id     if ($item) // check object has been returned     {        return $item->getsomething() * 2;     } } 

is true 1 benefit can presume object exist, there no need check if does?

it's called dependency injection, , main benefit can test dosomething() method in complete isolation injecting "mock" item object method, testing dosomething() isn't dependent on logic of item itself