If you're stopped by the police and don't have a license on hand, you could face a little trouble. However, that trouble is nothing compared to the difficulties you'd face if you did not have a license at all and yet decided to drive a car.
The reason people have to get licenses is because it proves that they're educated in traffic safety and can manage to drive a vehicle safely. If your license is revoked or you never apply for one, there's no way for the police to know that you're able to drive safely. You'll likely face arrest if you do not have a license.
If instead you simply forget your license, you likely won't be arrested, but you'll need to provide proof that you have a license as soon as possible.
What kinds of penalties can you face for driving without a license?
If you drive without a valid license, you could face a citation, arrest or be charged with a misdemeanor. In New York, for example, you'll be charged up to $300 for operating a vehicle on an expired license. If you do not have a license, it's possible to face misdemeanor charges initially or felonies if this has happened several times.
Is there ever a reason to drive without a license?
You should never drive without a license, but there may be circumstances where the risks don't outweigh the benefits. For instance, if you have to drive under threat or because there is an emergency, the authorities may be easier on you than if you were driving without a license just because you felt like it.
Source: FindLaw, "Driving Without a License," accessed May 09, 2018