Everything that you can do to a Unicode string, except concatenation, is defined in terms of code points. Normalization, case transformations, collation, regexes, layout and rendering and encoding.

For example, let’s say you want to define a “natural sort” order that sorts e.g. “A2” < “A10”. To do that you divide the string at boundaries between code points in ranges of each numeral type that you are supporting (e.g. western numerals, Arabic numerals, Chinese numerals).