I couldn't find any authoritative references about this which are available on public internet.
the code is
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It's pretty subjective once you get into different widths of spaces down to such minute details. I don't believe you'll find a specific usage because one does not exist.
The main difference among other space characters is their width. U+2000..U+2006 are standard quad widths used in typography. U+2007
FIGURE SPACEhas a fixed width, known as tabular width, which is the same as digits used in tables. U+2008
PUNCTUATION SPACEis a space defined to be the same width as a period. U+2009
THIN SPACEand U+200A
HAIR SPACEare successively smaller-width spaces used for narrow word gaps and for justification of type. The fixed-width space characters (U+2000..U+200A) are derviced from conventional (hot lead) typography. Algorithmic kerning and justification in computerized typography do not use these characters. However, where they are used (for example, in typesetting mathematical formulae), their width is generally font-specific, and they typically do not expand during justification. The exception is U+2009
THIN SPACE, which sometimes gets adjusted.
Again it makes no difference if its in French. The only exception are the non-breaking spaces used to distinguish words in languages that don't generally have spaces between words.
Based on what you're asking I would use unicode values when entering data or content into a database and you are offering an API or someone needs to pull data from the API. Actually rendered characters can cause issues over time or depending on how the code is written can cause catastrophic effects to the rendered output.
Another reason you would use unicode is if your font doesn't actually have the character present and the browser would still be able to render the value correctly based on the unicode.