2nd what
@ChebyshevII PE said. All this varies from state to state.
You have to renew periodically and pay a renewal fee.
In general most states require continuing education. How much and how often varies. You generally have to provide a log every time you renew, and sometimes people get audited and have to provide additional proof.
If your job doesn't require a PE, then you can do whatever you want. But keep in mind that reinstating an inactive or expired license is not always quick and easy. Again it varies from state to state, but you might have to prove that you have already met the continuing education requirement. You may have to pay application fees, penalties, etc that actually cost more than keeping it active (depending on how long it's been inactive).
Also keep this in mind if you do decide go inactive/expired. Obviously you can't stamp things (i.e. practicing without a license). But also you're probably not allowed to refer to yourself as a PE (misrepresentation). Make sure you remove it from your resume, your LinkedIn profile, your business cards, your email signature, etc. Boards often punish people for misrepresenting themselves.
The thing I want to make sure you take away is
Make sure you know all the details and the implications/consequences before you decide what you're going to do.