There are people who have cracked the top of a steering tube, hence the suggestion to use a 5mm spacer and extend the steerer 2-3mm above the stem. There are also those who worry about over tightening the expanding plug, or leaving it too loose and slipping. The newest plugs sit on top of the steerer and force the use of a spacer on top. I like no spacer above the stem. This solves all of those problems. It might take 30 minutes to do, but I find it worthwhile. To each his own.