Space Reclaim in words

Thin Disks

VM server
Windows
50GB Disk C:\

Guest
Zero in guest WILL fill the disk
sdelete -z C:\

VMDK will be 50GB
Guest will be 0GB
Storage Will be 0GB IF it understand Zeroing

To resolve VMDK size
Storage Vmotion
or
vmkfstools -K /path/to/disk-name.vmdk

https://kb.vmware.com/s/article/2004155

or the best soloution run in-guest UNMAP
BUT
Virtual disk must be thin
Windows you need ESXi 6.0 or greater
Linux you need ESXi 6.5 or greater
CBT must be off if you are running older than 6.5
CBT can be on but you must run 6.5 or greater
NO snapshot
VMFS-5 ESXi option EnableBlockDelete must be enabled if you want UNMAP to be sent to the array
VMFS-6 ESXi options automatic reclamation must be enabled must be enabled if you want UNMAP to be sent to the array

Windows:
Optimize Drives

Delete VMDK from storage

ESXi 6.5
Automatic

Lower than 6.5
Manual with unmap command

Thick Disks

VM server
Windows
50GB Disk C:\

Guest will report what is in use
VMD will always report 50 GB
Array depends

For the Array to mirror the real use you can
Write Zeros
sdelete -z C:\
UNMAP is not availble because the disk is thick

Delete the vmdk
use UNMAP on the esxi