As usual, I have to agree with Sheldon, but I would add that the reason I leave the stem loose enough so that I can twist the bars with the front wheel between my legs, is that in a crash, the front wheel can turn enough so that the bars hit the top tube. On a steel bike, the bars can ding the top tube but if the stem can move, less chance of a ding.
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Il faut de l'audace, encore de l'audace, toujours de l'audace
1980 3Rensho-- 1975 Raleigh Sprite 3spd
1990s Raleigh M20 MTB--2007 Windsor Hour (track)
1988 Ducati 750 F1