As mentioned, the reasoning is about supporting the steerer tube. Personally, I wouldn't worry too much about it.

Some expansion plug assemblies offer no support to the steerer tube,a nd you don't see steerer tubes using those plugs failing.

Conversely, I can see that the glued in aluminum sleeve type could offer some support, and all else equal why not take advantage of it, if you can.

Thus, I'd follow C'dales recoomendation, once I had things dialed in. But I wouldn't hesitate to put spacers above the stem, on a temporary basis, being careful not to overtorque the stem.