What are the use cases for a full node, if the lite node is sufficient for most of the byteball activities? Is it possible to bootstrap the full node with a separate download of the 10GB files, like many other wallets do?
Lite is sufficient for most cases. Full node is considered better for privacy in the same way a bitcoin full node is (so to speak). Full node has a very few reasons to be run.
There is not a bootstrap capability that I know of; but....
You can find someone that has a full node synced and:
1) willing to make a backup so that you could restore. Then, you could delete the user data in order to restart as a full node in which is creates a new wallet which is already synced.
or
2) willing to zip up the directory (except the user data). Then you could start the app and select full node.
In either case, the above (backup or zip) will take 2GB of space compressed.