Storage+Compute: Existing vSAN clusters can be expanded by adding additional vSAN nodes, which adds additional compute and storage resources to the shared pool.
Compute-only: When the vSAN VMkernel is installed and enabled on a host that is not contributing storage but resides in the same cluster as contributing hosts, vSAN datastores can be presented to these hypervisor hosts as well. This is also beneficial to storage migrations as it allows for online storage vMotions between vSAN storage and non-vSAN storage platforms. The use of the vSAN VMkernel requires a vSAN license for this host.
Storage-only: N/A; A vSAN node always takes active part in the hypervisor (compute) cluster as well as the storage cluster.