VG keeps track of all the Clips in your collection in several different files.
Think of these files as your collection database.
They don't hold the actual Animations, but they hold information about what clips are downloaded, what clips you have the rights to play, what Demo's are on your carousel
Rebuild All, tells VG to Re-download the Rights from the server, and to Verify that the Clips are actually present in the folders, and updates the Database accordingly.
It also used to Reset the Demo's rotation back to the very beginning.
(I don't know if it still does this or not)
Sometimes the GUI, Downloader, and the Database can get out of sync.
The GUI thinks a card is Downloaded, but it's not written to the database.
The Downloader attempts to download the same card and gets stuck, and the rest of your downloads sit there waiting..
To Fix that type of trouble.
You locate the Stuck Download and delete it.
Then you Rebuild all, so it's all synced back the way it should be.
If you have the Automatic Download check marks checked, this could also result in cards beginning to download. ( ones that haven't been downloaded yet)
Also Keep in mind that the P2P download process is Different from the Server Download process.
P2P will make a place holder that has the same name and size as the Fully downloaded file.
As P2P makes connections, it gets small pieces from different sources and fills in this place holder.
Sort of like building a puzzle one small piece at a time.
The Server side Download Builds the File in a continuous stream from start to finish.
So as the file is downloaded the file size increases a little at a time.
It has a temporary file name, until it is fully downloaded, then it is renamed.