Originally Posted by
speedevil
I guess I'm asking if riding it without the plug in place inside the steerer is OK, for just a short while to check the fit.
The expansion plug supports the stem. I would not tighten the stem without the expansion plug in place. It is very easy to crush the steerer to the point where the carbon delaminates and cracks.
People are free to make their own choices but please watch this video before you decide. At least watch the first two minutes.