It often happens that you have non-Roman text data in Unicode, but you can't
display it -- usually because you're trying to show it to a user via an
application that doesn't support Unicode, or because the fonts you need aren't
accessible. You could represent the Unicode characters as "???????" or
"\15BA\15A0\1610...", but that's nearly useless to the user who actually wants
to read what the text says.

What Text::Unidecode provides is a function, unidecode(...) that takes Unicode
data and tries to represent it in US-ASCII characters (i.e., the universally
displayable characters between 0x00 and 0x7F). The representation is almost
always an attempt at transliteration -- i.e., conveying, in Roman letters, the
pronunciation expressed by the text in some other writing system. (See the
example in the synopsis.)