The 8.0.4 is for current production and provide only the base functionality for the NAS. The 8.2 version is in Beta and provides plug-ins in order to restore the functionality that was in 7.2 and was removed for the complete rewrite of FreeNAS.
If you only care about the NAS element use 8.0.4 until the 8.2 is released.
The plugins will include print-server, bit-torrent, media server and many others known and those yet to be developed.
I hope this helps.