When you apply for and receive a visa to visit or work in the United States, it generally has effective dates on it. It's only between one date and the next that you're permitted to travel within or remain working in this country. If you overstay the expiration date listed on your visa, then you may be subjected to various types of disciplinary action including jeopardizing your ability to return to the U.S.
The type of disciplinary action that you'll receive in such instances all comes down to how long you overstayed your visa's expiration date. Time begins "tolling," or accruing the minute that a visa holder overstays their visa. An immigrant may first have to wait whatever amount of time is tolled before they can return to the U.S. if they wish to return once again.