Superscript Latin Small Letter I

Its role comes from the expression it modifies.

In Latin writing, raised letters marked contractions and abbreviations. Medieval English manuscripts show superscript-i uses from the late twelfth century; that evidence dates the writing convention, not this encoded character.

Is ⁱ the same as formatting an i as superscript?

No. ⁱ is a character; superscript formatting is a text style.

For equations, documents, and footnotes, formatting an ordinary i lets software control its size and position. Use ⁱ when plain text itself needs the raised form.