When you're using thick-provisioned disks, space is pre-allocated on the storage array. So if the .vmdk is 500GB, but you're using only 200GB within the OS, you will still be consuming 500GB on the storage array.
Then if you delete the VM from a thin-provisioned LUN, space will not be reclaimed back, unless you're running vSphere 6.5 which introduces automatic UNMAP.
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VCIX-DCV, VCIX-NV, VCAP-CMA | vExpert '16, '17, '18
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