Insurance companies are some of the largest corporate institutions with large budgets and compelling reasons to invest in prevention of fraud of all kinds - from insurance coverage to recovery of damages. This clearly applies to how a larger number of insurance companies handle injury claims today. The insurers invest resources into studying injury claims (especially the ones that are alleged to be serious) and among other things, determining with the help of highly qualified nurses and doctors whether the medical treatment an injured person received was "reasonable and necessary." These are magic words when it comes to proving damages in court or determining the settlement value of an injury case. 
An insurer who discovers that the claimant treated far longer and far more frequently than he likely should have, considering the injuries sustained, will look closely at the nature and the cost of treatment received. If the treatment is clearly excessive and more expensive than it should be, the insurance company will use that information to cast strong doubt on the claimant's credibility, making him/her look like someone who is trying to treat more than needed and inflate claims for the sheer purpose of increasing recovery. This argument works quite often to reduce a claimant's recovery or event lose the case in court where they otherwise could have won. This is because few factors hurt a party in trial in front of a jury than credibility issues. Once the jury determines or event suspects that the claimant treated more than he needed for improper reason, they likely will doubt the entire claim and won't believe much else of what the claimant has to say on the stand. This is exactly the reason why it's a good idea to avoid getting more medical care than you need for your injuries, especially if your case is likely to go to trial. 

You should especially make sure you don't get too much of the treatment that doesn't help you. Therefore, if for instance you treat for a chiropractor for 1-2 months and you feel no improvement in your pain symptoms, you should at least consider switching to physical therapy, acupuncture, etc. This is because it's usually quite hard to explain why a person went to see a particular doctor for 6 months or more several times a week if it didn't help at all. 

Any "serious" attorney who handles bigger injury cases and facing a real likelihood of jury trial knows that regardless of the facts of his client's case and his injuries, his case to a great extent depends on his client's credibility. The impression that the injured plaintiff gives to a jury is critical to his ability to recover compensation. A typical juror has his own pains and problems and is inherently skeptical of the pain of other people. Any well founded suspicion that you exaggerate your injuries and your treatment is inflated will make you come across as a whiner who probably exaggerate just about everything he says and will make the jury far less generous than they would have otherwise been. 

Remember, a hero stops being a hero as soon as he considers himself one. The physical pain you are suffering, as well as your emotional distress as a result of the pain is something that the jury / defense attorneys have to infer indirectly from what happened in the injury incident and not simply take your word for it. 

This means that treating longer than you reasonable should have to simply increase the amount of medical bills, or having your doctor write a report to grossly exaggerates your symptoms and injuries will likely backfire at a deposition, when it's time for you or your doctor to testify or later - at trial. This means that you should not treat longer than you feel is necessary, and you should not continue seeking the same type of treatment of too long if it proves to be ineffective.