Need for space reclamation will be needed of there are following situation.
1. If there is a thin lun from the storage and you have deleted few vms or did a storage vmotion.
2. Esxi host does not do auto spce reclamation because it is an over head for hostd and vmkernel.
3 if you have VAAI feature then it can happen automatically because host will offload the task to the storage.
Starting from vSphere 6.5 these reclamation tasks are automated. with the HW version 11 the new SCSI adaptor will send the unmap command to guest OS and if the guest OS supports this unmap it will work.
We have a GUI option to unmap the datastore unused space. also, you can set the interval how frequent this unmap should run.
Hope the following article will help you to get more details on this
Further to your question. Guest OS UNMAP is supported for Windows Server 2012 and later with VM hardware version 11 and for Linux with VM hardware version 13.
Hope that helps.