It often happens that you have text data in Unicode, but you need to represent
it in ASCII. For example when integrating with legacy code that doesn't support
Unicode, or for ease of entry of non-Roman names on a US keyboard, or when
constructing ASCII machine identifiers from human-readable Unicode strings that
should still be somewhat intelligible (a popular example of this is when making
an URL slug from an article title).
In most of these examples you could represent Unicode characters as ??? or
\\15BA\\15A0\\1610, to mention two extreme cases. But that's nearly useless to
someone who actually wants to read what the text says.
What Unidecode provides is a middle road: the function unidecode() takes Unicode
data and tries to represent it in ASCII characters (i.e., the universally
displayable characters between 0x00 and 0x7F), where the compromises taken when
mapping between two character sets are chosen to be near what a human with a US
keyboard would choose.
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