There are hundreds, if not thousands of spells on this site that will never work. As an example, none of the spells in the Trick and Fantasy sections work. Sunni is correct that magic is not going to create a physical change in your body, nor will it make you turn into something other than human, permit you to fly, and countless other things straight out of fictional books or Hollywood films. Magic is far more subtle than that.
Anyone of Council rank in a Coven can add spells to the site, and in Spellcaster's Coven every member is Council. So a lot of nonsense gets added over time. The Moderators do not have the ability (not to mention the time) to remove all of the nonsense spells. So it's up to the individual to use their common sense and decide whether something would be possible or not.