Transformations have the role of frightening us by showing that appearances deceive. Sometimes things seem one thing, but the transformation reveals that it is another and the purpose of this is to surprise us.
You'll have to be somewhat more specific with regards to what form of transformation you refer to. Shaper shifter, red riding hood and the wolf, multiple personality disorders, serial killer etc... The one common thread in this context is that appearances are always deceiving so it is always wise to be on your guard in any given situation because absolute safety is an illusion.
