"...VM recommends using VSAN over dedicated storage..."
I think your asking what VMWare recommends. And it .. as most things is "depends on what your trying to do.
Local Disk:
-Pros: Simple. Fast. VMs predictable in location to start up. you can use older / mixed performance disk types and still works. Good if your doing scale out application design where application maintains availability by its replication or scale out design. Also cost effective as you can learn to use VMWare ESXi /vCenter on cheap for basic VM hosting
-Cons: No vMotion, HA, DRS to protect or recover VMs. to move VM without export / extraction / copy . Not really reflective of production design most people would use, shared VMFS volumes are core to the design ROI of VMWare's hosting stack.
vSAN:
-Pros: Use of internal disk to get "SAN like features" of mobility, HA, DR, predictive maintenance. License for this for many customers is far better ROI then external NAS/SAN storage. Can scale organically as you add more block disk. Can provide very cost effective "datacenter class hosting environment"
-Cons: Must have at min one SSD but most due to latency all SSD very helpful. Most environments need 10Gb / higher throughput LAN for block. More complex and has repair / recovery complexity. Is more brittle in repair then separated SAN / NAS external storage. Compute repair / reconstruction is coupled with also repair / recovery of data.
SAN: (bonus round)
-Pros: Disk separated and can be designed direct for explicate use case and needs (Replication, performance, capacity per $, redundancy, network topology and transport types etc.). Very mature for support.
-Cons: Cost to maintain independent storage tier and resources. Cost of maintenance of external subsystem and its unique and specialized support overhead.
My though is: Do you need vMotion and shared storage.. Then vSAN.. or SAN needed. Do you want lower cost and integrated systems / storage.. vSAN. Do you have ROI where external dedicated storage .. then go with dedicated external SAN vendor (and that which one is entire side thread).
My $.0002
PS: this is not all encompassing of pros and cons.. just top ones.