There are many reasons you could need setting file and folder ownership on a Windows file server. In my case I had to take care of the file ownership because I have been migrating our users' home folders to a NetApp volume with user quotas set. A quota is intended to limit the amount of disk space and the number of files that a particular user or group can consume. As far as I have understood, Netapp quota application mechanism is not based on home folders size but, and this is new to me, on real file ownership.
In fact, as stated on the NetApp website, quota calculation of NTFS qtrees is always allocated to the user’s Windows SID. This means that the NetApp is aware of all the files that belong to a user no matter where they are located on the volume. So, even if these files are scattered about your file system and not located in a single place, the NetApp will be able to tell you exactly how much space is allocated to a Windows user (through his SID) via the "quota report" command.
Unfortunately, in my case I had robocopied all the contents and ACLs from our old Windows file server to a brand new NetApp filer and discovered that the NetApp wasn't reporting any user quota. This is due to the fact that I did not had copied the owner flag when I used Robocopy and so the filer reported that every file was owned by builtin\administrators... and that no user quotas where enforced...
|File ownership tab under Windows Security|
After a short investigation I found out that I had to re-apply correct file onwership for the filer to be aware of real user quota usage.