This (of course) depends on the specific circumstances you are faced with. As a general rule, however, insurance companies take claims much more seriously when the injured party is represented by a personal injury attorney. Having an attorney will allow you to obtain information about the best way to proceed with your claim and what you should do to avoid being taken advantage of.
If your legal claim cannot be settled you will need to file a lawsuit to recovery for your losses. Litigating a lawsuit without an attorney would be a very bad idea. The rules of civil procedure are complicated and require experience and study to ensure that mistakes are not made. It would be like trying to build a house without any training in carpentry. Most important, having a lawyer should allow you some peace of mind that your claim is being properly handled.