Formulas, units and footnotes
Superscript numbers are perfect for exponents and units: x², 10⁶, m³ or cm². Subscripts handle chemistry and maths indices, as in CO₂, H₂SO₄ or a₁, a₂, a₃. Writers also use ¹, ² and ³ as footnote markers in plain-text articles and social posts. Because each one is a real character, the formatting survives copying, pasting and sharing.
Why some letters are missing
Unicode offers superscript forms of almost every lowercase Latin letter, but subscript letters are limited to a handful such as ₐ, ₑ, ₒ, ₓ and ₙ. Capitals are patchy too: there is no widely supported superscript C, F, Q, S, X, Y or Z. That is why tiny-text generators sometimes swap in look-alike characters, and why letter sizes can vary slightly from font to font.