Is Airstone Necessary For Filtration?

[Dr.Rock]

Is an airstone necessary at the end of an airline (in uplift tube) for an under-gravel filter? Or can I do without the airstone and just have large bubbles coming out from it? I thoough the airstone may restrict the airflow and therefore lower the water flowrate through the gravel. Is there any advantage with the stone, producing fine bubbles rather than large bubbles?

Thanks.