Many Green Card holders (Lawful Permanent Residents) choose not to become Naturalized Citizens for many years. There is nothing wrong with this but there are some very basic benefits to Citizenship which could come in useful. First, you cannot vote if you are not a U.S. Citizen. If you didn’t know this and you do vote, be aware that this can cause you to be deported. Further, not getting to choose if your next elected representative or president will help or hurt immigrants could have a direct impact on you.
Second, not everyone lives a perfectly peaceful and quiet life. Every once in a while, often when least expected, trouble arises and the best of people find themselves arrested or charged with a crime. Of course, you will need a good criminal defense attorney to help in this situation, but some criminal charges can also lead to deportation. However, those who have been granted U.S. Citizenship do not face these repercussions. Only Lawful Permanent Residents are subject to deportation for specific enumerated crimes or for something called crimes of moral turpitude.
Third, Lawful Permanent Residents cannot travel freely outside of the U.S. for extended periods of time without abandoning their green card status. If you travel for up to six months at a time, you are safe. However, if you need to stay outside of the U.S. for over one year, and you fail to get permission by applying for an I-131, you can be deemed to have abandoned your Lawful Permanent Resident status and may be prevented from returning to the United States.
Once you are a Naturalized Citizen, none of these issues will apply to you any longer. It is very rare for the U.S. Government to denaturalize a Naturalized citizen and the reasons for doing so will be far more limited than those that can cause deportation for a green card holder. For an interesting example, see the following story of a Cleveland man who lived peacefully in the U.S. until he was denaturalized and deported for suspected war crimes.