Both use XYZ::XS; and require XYZ::XS; load the dll in exactly the same way (by using LoadLibrary on Windows).

The only difference (afaik) in the loading of the dll is in *when* it happens. If you use XYZ::XS; then the loading is done at script compile-time (whenever the compilation process gets to that compile-time command).
And if you require XYZ::XS; then the loading is done at script run-time (whenever the execution process gets to that run-time command).

Cheers,
Rob