While the bathtub method is not officially recommended by hotels, pest control specialists acknowledge that it is certainly one of the safest temporary spots to place your luggage while you conduct your room inspection.
What seems like a strange or random thing to do is actually a very smart precaution that comes from real-life experience. Guests who put their luggage in the bathtub are not being odd—they are simply taking steps to protect themselves from possible bed bug infestations, unexpected water damage, or general cleanliness issues.