245(i) provisions
Here's the particular thingy about leaving the US if you're under 245(i):
2. Who can benefit from the new Section 245(i) provisions?
A person who is eligible for permanent residence based on a family relationship or job offer, and who wishes to adjust status to permanent residence without leaving the U.S., could benefit from these provisions. Without Section 245(i), most persons who entered the U.S. without inspection, overstayed an admission, acted in violation of the terms of their status, worked without authorization, entered as a crewman, or were admitted in transit without a visa would not have been eligible to adjust status in the U.S. If an individual is eligible for permanent residence, but not eligible for adjustment of status, that person might still obtain permanent residence by leaving the U.S. and completing the process for an immigrant visa at a U.S. consulate abroad. However, if that individual had been unlawfully present in the U.S. for more than 180 days, he or she would be barred from reentering the U.S. for at least 3 years, and perhaps as long as 10 years. Under Section 245(i), an eligible individual can remain in the U.S. to obtain permanent residence through adjustment of status, and thus never trigger these entry bars. (Once permanent residence is obtained, these entry bars no longer apply.) Thus, it is particularly important that persons who would be subject to the bars not leave the U.S. at all until the adjustment of status process is completed.