One great example of this is the Gumtree site[0]. The social media share buttons at the bottom only load in when you hover over them (with the placeholder being Gumtree-styled social media icons). Great for performance and privacy (although I would prefer no buttons / social media code at all). I've always been really impressed by this, I wish more sites would do it.

[0]: https://www.gumtree.com/