MARCXML - What is it for?

Hi all,

I've just spent the last couple of weeks delving into and decoding a
binary file format. This, in turn, got me thinking about MARCXML.

In a nutshell, it looks like it's supposed to contain the exact same
data as a normal MARC record, except in XML form. As in, it should be
round-trippable.

What's the advantage to this? I can see using a human-readable format
for poorly-documented file formats -- they're relatively easy to read
and understand. But MARC is well, well-documented, with more than one
free implementation in cursory searching. And once you know a binary
file's format, it's no harder to parse than XML, and the data's
smaller and processing faster.

So... why the XML?

Curious,
-Nate