Many states are "at-will" meaning an employer can "terminate an employee at any time for any reason, except an illegal one, or for no reason without incurring legal liability." However, you as an employee are also "free to leave a job at any time for any or no reason with no adverse legal consequences." Meaning: You are not required by law to give two weeks notice of your intentions to quit.
They can fire you, you can fire them. That simple.
Federal law does not require employers to provide final pay immediately when an employee quits, but some states do. Check with your State Labor Office at the link below. Some states have time limits based on when you were fired, others have time limits based on when you resigned.
Additionally, some states have rules requiring employers to pay out unused vacation days with the final paycheck. If your employer does not provide "unlimited PTO" (also known as "flexible PTO"), you might be owed whatever time you've accrued in vacation time if you haven't used it.
If you're leaving a shitty job for a better paying one, delaying your exit by two weeks could mean missing out on extra earnings. A worker is earning $20 an hour and manages to land a new job at $25, will lose $400 in those two weeks.