Profiling is a very valuable tool in ascertaining what "type" of suspect you are looking for but without a suspect in mind to begin with it's not that useful.
The source of the profile is important - anything from the FBI BSU is more reliable than say one that your Aunt did.
However, the main thing that can make a profile inconsistent or unreliable is the evidence used to make the profile. If assumptions or speculation are used the profile is likely to go in the wrong direction.
A good example of this is the child murders in West Memphis, Arkansas. Famed profiler John Douglas originally stated that he believed cults or Satanic activity could be involved due to what were perceived to be ritualistic genital mutilations on the victims. This was information he was provided by an unreliable coroner. Years later when the evidence was re-examined a different pathologist came to the conclusion that those mutiliations weren't ritualistic at all and were actually the result of animal activity that took place where the bodies had been dumped and were not part of the crimes at all. With this new information anything about ritualistic mutilations was removed from Douglas' report and he revised his profile to someone who the victims probably knew and it was totally different. He was only working with the information he was provided by the investigation and he had to trust that those investigators knew what they were doing and that their evidence was valid.
With JtR you can find similar inconsistencies on inquest reports. Did the killer have anatomical knowledge? Did he have medical knowledge? Did he show evidence of being butcher? All of these comments have been unsubstantiated and not been viewed as reliable but you can see how if somebody creating a profile took the coroner's word that the killer had medical knowledge then that would drastically reduce the scope of the profile and focus on a smaller number of suspects that could quite easily be incorrect purely because of the initial unreliable piece of evidence that went into creating the profile.