In the US, companies are not required to give severance packages when doing layoffs. Check your local states' labor laws, as it may differ, but most states simply follow Federal Guidelines and there isn't a Federal requirement.
The federal Worker Adjustment and Retraining Notification Act (WARN Act) requires employers to provide 60 days' notice, during which all wages and benefits will continue to flow as usual, giving those who were laid off at least a little time to brace for unemployment, or get busy finding that new (better — knock wood) ...
Severance is never a requirement of any employer unless you have a signed employment agreement stating otherwise, or, it is a written policy of the company.
Lump sum severance package cons Lump sum payments may push you into a higher tax bracket for that year. You need to manage your finances more carefully to ensure the lump sum lasts until you secure another source of income. Finally, you forfeit any negotiation power for future benefits or assistance.