Empty space is doing real work

Whitespace isn't what's left over after you place the content. It's what holds the content up.

Margin, padding and line-height are the load-bearing elements of a page. Pull them out and the relationships between everything else collapse: titles stop reading like titles, sections stop feeling like sections, and rhythm becomes a wall of text.

Why it almost always survives the edit

When the brief gets tighter, decoration goes first. Type contrast goes second. Whitespace, if it was earned, survives — because the moment you take it away, the page tells you, loudly, what you just lost.