There are two benefits of advance parole: First, it enables an alien to return to the U.S. after traveling abroad without the necessity of obtaining a visa.  Second, it preserves whatever Adjustment of Status (I-485) applications the alien has pending at the USCIS.  When aliens are paroled outside of the U.S., all pending applications, such as the application for adjustment of status, continue to be effective.

Please note that aliens holding valid H-1 (temporary worker in a specialty occupation) or L-1 (intra-company transferee) visas and their dependants who have filed for adjustment of status do not have to file for Advance Parole for the purposes of maintaining their adjustment of status application, as long as they do not run out of non-immigrant status before returning to the US. However, in this situation, they still need a valid H-1 or L-1 visa to come back to the U.S

For more information on Advance Parole, please click on the following links:
What is Advance Parole?
What are the benefits of Advance Parole?
Who is eligible for Advance Parole?
What documents and information are needed for applying an Advance Parole?
What is the difference between an Advance Parole and a Re-entry Permit?
H-1 B Visa and Advanced Parole
Frequently asked questions about Advance Parole
Attorney's fee and filing fee
Advance Parole Issue in Latest Z&A Memo
Memo: Be Aware of Abandonment of COS and AOS Applications