getModuleById parameter parsing

Question

So when getting a module for rendering inside a component this is not working:

$mod = ModuleHelper::getModuleById(123);

but this:

$mod = ModuleHelper::getModuleById("123");

That's because inside Joomlas getModuleById function the type is declared to string:

if ((string) $modules[$i]->id === $id) {

Does that makes sence? Whats the purpose of that?