The movement is a necessary stimulus causing the tree to alter it's growth to compensate.  The tree is a self maximising organism and needs the stimuli to produce a reaction.  Absent of the movement or stimuli there is no need for the tree to increasing trunk diameter and root growth.  In addition to affecting the trees growth the stakes can also damage the tree.  They can become embedded in the tree interfering with vascular tissue and causing structural problems.  If the stakes are to be left on for an extended period (more than one year) they should be inspected and adjusted to avoid damaging the tree.