What it gives you
The right to live and work permanently, to travel, to petition for certain relatives, and after a qualifying period the possible option of naturalization. It does not give you the right to vote in federal elections, and it does not make you a citizen.
It can be abandoned
Extended time abroad can raise the question of whether residence was abandoned. Intent matters, and so does documentation: ties maintained, taxes filed as a resident, a home, employment. A re-entry permit exists for planned long absences and has to be applied for before leaving.
It can be lost through conduct
Certain criminal matters, and fraud in obtaining the status, can lead to removal. Immigration consequences do not track criminal outcomes, so advice before a plea matters.
Practical obligations
Keep the card valid and renew it on time. Report address changes within the required period. File taxes as a resident. These sound administrative and they are the things that create problems years later at naturalization.
