Oh right then the savings will be a bit less. Just ran a test with the latest version on GitHub without any changes:
- Standard Arduino IDE with Leonardo 26614 bytes
- Homemade package Arduboy - Standard core - 26604 bytes
- Homemade package Arduboy - Arduboy optimized core - 26398 bytes
With the Arduboy optimized core you also have the bootloader/reset button feature in case you decide to remove the USB code.