With json, you'll loose support for __sleep() / __wakeup() methods and type information. Without additional work, json will decode everything as either assoc array or as stdClass. This means you can't make both of these work:
```php
assertSame( $assocArray, load(save($assocArray)) );
assertSame( $stdClass, load(save($stdClass)) );
```
I'm not sure about the size, don't think serialize will store attribute names for every instance?