I frequently see small trees staked with some support twine or rope, presumably to aid against strong winds.
However, I've heard or read somewhere that staking small trees can actually be harmful, preventing them from building a natural resistance to the wind (in trunk strength, root development, etc.)
There are many guides that explain "proper" tree staking:
It seems, from aggregating information in such guides, that staking is sometimes necessary, but that people often do it wrong.
The question then, is how do you determine when to stake a tree (if at all)? Are there lots of oddly bent or fallen trees somewhere from lack of staking? I've never seen one.