The H-1B COE case (also known as an H-1B transfer) allows an employer to hire a foreign national who is in H-1B status for another company. What is unique about an H-1B change of employer case is that the new employer does not have to wait for the H-1B COE petition to be approved before allowing the foreign national to commence work. The employer can choose to begin employment of the foreign national once the H-1B COE petition is filed with USCIS.
Another unique component of an H-1B COE case, is that most cases are not subject to the H-1B quota limits. There are a limited number of new H-1B numbers available each year. Once the numbers are exhausted, no new H-1B petitions can be approved for that fiscal year. Most H-1B COE cases are not subject to these H-1B quota limits since the foreign workers were usually counted towards the H-1B quota with their initial H petition.