There are many reasons to use an attorney when you've been injured in an accident. The first and foremost reason is that you need someone to evaluate the value of your claim.

Insurance agents sell insurance. They are paid commissions on the amount of insurance they sell. They are usually helpful in trying to make a claim and usually want the company to make reasonable and prompt payment so you will stay with them. They do not evaluate or make decisions about paying your claim. That is done by an adjuster, usually a company employee, but on occasion an independent adjusting company.

The adjuster must evaluate and report to the company an estimate of the value of the claim. If they do not have all the information this can be a serious problem to getting the matter settled later on. 

Only an experienced attorney can fight over the proper value of your claim. Otherwise you are left with just the adjuster, an employee or contractor, deciding the value. Your attorney must be ready and able to try your case before a jury should they not agree to a reasonable value.