When a cluster is attached to a pool, cluster nodes are created using the the pool’s idle instances which help to reduce cluster start and auto-scaling times .
If you are using pools and looking to reduce start time for all scenarios, then you should consider keeping a min idle count equal or greater than the min nodes of the cluster. This will allow you to have machines available and ready to use when the cluster starts. If you have 0 machines on idle then the first job executed against the pool will have to wait for the VMs to become available.
