What does "Windows icon custom size" do?

I am using IP version 5.00.021.

My OS is Windows 7 Home Premium 64 bit.

I have been using IP5 since it came out and at no time has Settings-> System Settings -> Windows Settings ever been an active option.

Is the desktop icon size restricted to the "classic", "medium" and "large" sizes offered when right-clicking on the desktop?

I seem to remember older versions of IP allowing users to scale the icon size by selecting a pixel size.

Does this have something to do with the fact that IP is still 32-bit?