Permanent is not permanent!
Many parts of our immigration laws in the U.S. do not make sense, and this whole permanency label is one of those things. When a person becomes a Lawful Permanent Resident, there are conditions that apply, and sometimes the Permanent Resident cardholder has not been told about those conditions or just simply did not pay attention.
The basic conditions on Permanent Residence are pretty simple.
First, you have to obey the laws of the land where you are now living. If you break the law, you may get kicked out of the U.S. through the deportation process. For many types of crimes, it may be one strike and you are OUT.
Second, you have to really live here permanently. This means that you make your permanent home in the U.S. We have many permanent residents who travel A LOT, but the basic rule is that the majority of the time needs to be spent in the U.S. and your home needs to be in the U.S.
If you or someone you know has trouble with these basic requirements of permanent resident status, get competent legal advice before it becomes a problem. If you are ever charged with committing a crime, get a lawyer IMMEDIATELY and make sure your lawyer knows your immigration status. If you ever find yourself contemplating spending more than five months out of the U.S. at a time, talk to your lawyer for advice before you make those travel plans.