Holy cow, I wrote a book!
Because that function did exist at one point,
although it doesn't exist any more.
The function in question was available only on Windows 95-series
versions of Windows.
It never existed on Windows NT or any of its successors.
But remember that shlwapi.dll was originally developed
for Internet Explorer,
which ran on Windows 95 as well as Windows NT.
Internet Explorer checked the operating system and called
the Windows 95-only function only after verifying that it
was running on Windows 95.
If it was running on Windows NT, then it never called the
function and therefore never stepped on the land mine known
Okay, so why does shlwapi still link to the function
long after the Windows 95 series of operating systems have
Removing a function, even a function that doesn't do anything,
even an undocumented function that doesn't do anything,
is a dangerous endeavor.
Suppose you have a program that links to the function,
but just like Internet Explorer, it is clever and checks
whether it is running on Windows NT before calling it.
If you remove the useless function from shlwapi,
then that program will
fail to load,
even though it never calls the offending function,
and now you have an application compatibility problem on your hands.
Since it's a small function that doesn't do anything,
it's a lot less risky simply to leave the function in.
Even though it doesn't do anything except fail.