Xiao baitu, please help me about re-entry permit(I131)

I looked USCIS web site, the re-entry permit is valid for two years. But you said if I leave US more tnan an half year, I need apply the permit. I couldn\'t find any time range on USCIS, the only words from USCIS is give below:

NOTICE to permanent or conditional residents whoremain outside the United States for more than oneyear: If you do not obtain a reentry permit and remainoutside the United States for one year or more, it may bedetermined that you have abandoned your permanent orconditional resident status.

Based on their words, I think if I come back U.S. within one year, I don\'t need the permit. If I leave U.S. between one year and two years, I need it.
Am I right? Please let me know your opinion, I don\'t know why everyone think we need the permit if we leave U.S. more than half year instead of one year. Thanks!