For adjustment of status (clients processing inside the United States), you can travel like normal on your current visa during the Labor Certification stage of the process. Once the Labor Certification is approved, you can continue to travel internationally using your valid visa, while the I-140 is pending and even after I-140 approval. However, unless you are in H or L status, you must remain in the U.S. from when the I-485 is filed to until you receive your I-131 advance parole. Once you receive your advance parole, you can then use the advance parole document to resume international travel while your I-485 is pending.
For consular processing (clients processing outside of the United States), you can travel around the world freely including the United States during the Labor Certification stage of the process. After the I-140 is approved, your ability to travel to the U.S. will depend on the timing. We generally recommend stopping any travel into the U.S. once the National Visa Center (NVC) has documentarily-qualified your Consular case, and sends it to the consulate for final processing. Your attorney can provide specific guidance regarding your travel plans.