There are some monetary benefits..
You can sponsor your family more easily and bring them over here, and save some money on trips, phone-bill etc. It cuts both ways though.
However one major benefit is that after if you retire and want to spend your last days in your old country, then you can get Social security checks only if you are US citizen. (This applies to countries like India. There are exceptions for some countries). If you have GC, you cannot get these benefits after leaving USA. It especially helps
if you can get dual citizenship.
Another benefit is that US govt. cannot deport a citizen for drunk driving.