Instead of directly using the video tag with the poster, I see some sites are using placeholder divs and they put a fake play icon on the div.

There is no video tag inside it. But when users click on the play icon, then they insert the video tag inside the div and video starts playing. Users don't notice what is happening. Visually there is no difference.

But I'm wondering if this something can be done for optimization. Could this affect speed in a good way?