leonAzul
Illuminator
Well, for a start they make a claim that there is "energy" or "chi" which can be affected by the placement of furniture.
Some so-called practitioners make such outrageous claims.
Others understand the metaphoric use of language and the sense that fengshui is no more than the systematic application of common sense, with regards to the use of space.
Granted, it does accommodate superstition, and perhaps for that reason it should be regarded with suspicion, yet it is no more wooish then any other mnemonic device.
As a method, it falsifiably yields some esthetically beautiful spaces.