Originally Posted by
clevername
Shortening steerer tubes isn't really a problem... if you're worried about adjustability, just put the spacers on top of the stem, and you don't need to cut it. It might look funny but you won't need to cut the tube.
But permanently riding like that does add some risk.
If, say you're out of the saddle, pushing hard and something in the drivetrain should fail, causing you to come down heavily over the bars, an uncut steerer protruding upwards has greater potential of doing damage than if it's sitting flush with the stem.
Also why it's sensible always to use a top cap, even if it's not strictly required once bearing preload has been set.