What is accomplished when you install a bounce entry in a leaf?

Under a normal migration, when a VM moves due to vMotion onto a leaf that does not have those EPGs and VLANs programmed, the will be deployed immediately. vCenter/ESXI host will send a GARP to ACI, the old leaf will bounce traffic to the new location of the endpoint and traffic/learning will occur. The bounce entry will stick around for a bit (about 5 minutes) and then be removed. The EPGs, VLANs, and Default Gateway will be deployed as soon as the move is detected and there will be little to no downtime (i usually see 0-1 ping loss, most of the time just increased latency)

https://supportforums.cisco.com/discussion/12394516/importance-your-management-network-aci-world