Shrinking capitals with CSS `transform: scale()` thins the strokes along with the size, making them look lighter than the surrounding text. True small caps are glyphs a type designer drew separately, so their stroke weight matches the lowercase around them.
`font-variant-caps: small-caps` uses a font's dedicated small-caps glyphs when available, and synthesizes an approximation otherwise. `all-small-caps` extends this to letters that were already capitals.
Traditionally used for acronyms (NASA, HTML) or to subtly emphasize an opening word — distinct from the surrounding text, but without the visual shout of full capitals.
When to use
Acronyms, a chapter's opening word, byline names — subtle emphasis. Setting an entire headline in small caps is usually too much.