Calling 911 is one of the primary steps after an accident. It's widely recommended and a legal requirement in most circumstances.  But people don't always report accidents, especially minor ones. And in some cases, drivers involved in major accidents choose to handle the matter between themselves.

Not calling the police after an accident is a mistake. 

Here is why:

You may have injuries that weren't apparent at the scene 

Typically, when someone is involved in a traumatic event, such as an accident, they experience an adrenaline rush, which can distract them from sensing pain. As a result, you may believe you are not injured after an accident. But after a few hours or days, when the effects of adrenaline diminish, you may notice you are injured.

If you had reported the accident to the police, the police report will serve as evidence to help you get compensation for your medical expenses. Without a police report, the other driver's insurance company may argue you sustained the injuries after the accident. 

The other driver may refuse to cooperate

When drivers decide to resolve an accident without the police or insurers, they usually agree on certain conditions. How the at-fault driver will pay for damages/ injuries and so on. 

If you opt for this, and the other driver refuses to cooperate, resulting in you filing a claim with their insurer, it will be your word against theirs. You can avoid this with a police report, as you will have reliable evidence against them.

A police report contains in-depth details about an accident that can help you establish a claim against the other driver. Thus, you should always call the police after any accident and obtain adequate information about your case.