From the filers perspective, a write and a delete operation are both a write operation. So we will have a discrepancy when a file is deleted inside a lun. The space will free in the file system contained within the lun, but the filer will not free any space.
There are several articles below from VMware that discuss this topic.
There is no need to "recuperate" the lun "whitespace" (it's basically irrelevant), unless you intend to shrink your lun, in which case you would have to create a new lun and vmotion from the old lun to the new lun. As a systems admin, you need to be concerned with the datastore usage. As a storage admin, you need to be concerned about your volume and aggregate usage.