Many accident victims mistakenly believe that the other insurance company is on their side. Nothing could be further from the truth. Insurance company adjusters (the employees assigned to handle your claim) receive specialized training in how to find evidence that the insurance company can use to downplay or deny a claim and are given bonuses if they save the company money. They will initially come across as very friendly and concerned about your case. They act this way hoping that they can convince you to accept a low-ball settlement and get you to sign a release on your claims. They often make promises about how they will take care of "all" of your medical expenses.
However, if your medical expenses turn out to be more than a small amount of money or if you try to receive payment for your lost income, the adjuster's true nature starts to be revealed. Calls don't get returned, bills don't get paid, etc. If you are lucky enough to get through to the adjuster, you will likely experience hedging and vague responses to your questions. One part of an adjuster's training is to intentionally stall and delay a case if it becomes apparent that you are seeking more than the low-ball settlement amount they've been authorized to give you. They do this because (1) as long as the insurance company is holding on to your money, their collecting interest on it, not you, and (2) delays result in evidence being permanently lost. The loss of evidence almost always works to the insurance companies advantage. You can be sure that during the months that follow an accident, the adjuster is diligently gathering evidence that will help the insurance company and hurt your case--they, of course, never tell you that.
One of the ways that insurance adjusters find evidence that will harm your case is by requesting that you sign a broad medical release. Recently, an insurance company used a medical release to obtain access to one of our client's mental health records--information that had absolutely nothing to do with the case. The insurer then tried to use the information it obtained about our client's depression to suggest that the pain she experienced was "all in her head." As soon as we took over the case, we immediately revoked the authorization, but unfortunately the harm was already done by that point.
For all of these reasons, it is critical that you speak to an attorney as soon as possible after an accident, before waiving any of your rights or making errors that can harm your case.