The main use case is doing maintenance on the host machine without incurring planned downtime. E.g. You may have multiple VMs running applications like sharepo

The main use case is doing maintenance on the host machine without incurring planned downtime. E.g. You may have multiple VMs running applications like sharepoint, exchange, zimbra, or whatever, all on a host. You want to perform some planned maintenance on the host, e.g. update the firmware, add memory, upgrade the hypervisor, etc. You place the host in maintenance mode and the VMs are migrated off the host onto another one within the cluster without having to resort to planned downtime.