In order for you to be considered as a lawful permanent resident (LPR), a green card holder must be maintaining a permanent residence in the United States.
If you are outside the USA for a period greater than 180 days, the US Immigration may start questioning whether the permanent residence has been abandoned.
Being outside the USA for such periods of time can also effect you when applying for U.S. Citizenship.
If your only makes an annual or biannual visit to the USA, it may appear over time that you are spending more time abroad than in the United States, and actually living living and working abroad and you are then in risk of losing your LPR status
So please make sure you stay more than 180 days a year in USA when you are a Green Card holder.