Most of the time, we know how wide the margin or padding between elements that we want.

When we use em, we don't need to adjust the margin and padding manually whenever we change the font size because it will follow the font size.

For example: If the font size is 16px and we set the margin to be 2em, then the margin will be 32px. And if we change the font size to 12px, then the margin will become 24px.

I hope this makes sense 🙂