All lawful permanent or conditional permanent residents must apply for a Re-entry Permit if they intend to be outside the United States for more than 1 year but less than 2 years. You must be physically present in the USA when you file the Re Entry Permit application (Form I-131) and complete the biometrics services requirement. And you should refrain from departing the USA until the Reentry Permit is finally granted to you. Though a Reentry Permit may be sent to a U.S. Consulate, U.S. Embassy, or DHS office abroad for you to pick up, if you make such a request. With the exception of having to obtain a returning resident visa abroad, a Reentry Permit does not exempt you from compliance with any of the requirements of US immigration laws.
So if you do not obtain a Reentry Permit before travelling abroad, lengthy or frequent absences from the United States can be considered as possible abandonment of your resident status. And if the Department of Homeland Security determines, upon your return to the USA, that you have abandoned your lawful permanent resident status, you may fall under determination procedure and further removal proceedings.
An absence from the USA for 1 year or more will generally break the continuity of your required continuous residence for the purpose of naturalization. In case you intend to remain outside the United States for 1 year or more, consider filing Form N-470, Application to Preserve Residence for Naturalization Purposes.