L-1 foreign nationals who are managers and executives are eligible for the 'priority workers' category. Foreign nationals falling into this category may apply for permanent residency without having to undergo the time consuming labor certification process.
If you are applying for Adjustment of Status to permanent resident, you must receive advance permission to return to the U.S. if you are traveling outside the U.S. This advance permission is called Advance Parole. If you do not apply for Advance Parole before you leave the country, you will abandon your application with the USCIS and you may not be permitted to return to the U.S.
Yes, if you are in a valid L-1 status you do not need an Advance Parole if you have applied for a Green Card. However, you must be coming back in to work with the same employer that applied for your L-1. Your spouse and children can also travel and the same rules apply.