Using an SSD persistent disk as a boot disk for your nodes offers some performance benefits:
Nodes have faster boot times.
Binaries and files served from containers are available to the node faster. This can increase performance for I/O-intensive workloads, such as web-serving applications that host static files or short-running, I/O-intensive batch jobs.
Files stored on the node's local media (exposed via hostPath or emptyDir volumes) can see improved I/O performance.
For additional information on how SSD persistent disks perform compared to, standard persistent disks, see the Block storage performance comparison.