Calamares 'Encrypt system' and 'Encrypt' partitions options?

The Calamares installer has an option to Encrypt system and also options to Encrypt individual partitions, which leaves me puzzled as to what Calamares does?

The system on which I am doing a fresh install is a manually GPT partitioned SSD as follows:

8MiB unformatted bios-grub
5GiB linuxswap
390GiB btrfs root /

What would be the difference between choosing to:

  • Encrypt system only
  • Encrypt the swap and root partitions only
  • Encrypt system and Encrypt swap and root

Would the last option mean swap and root get double encrypted?
Encrypt system implies swap and root would be encrypted anyway and not need to be encrypted individually but that the bios-grub partition would also get encrypted?

Sorry if I am confused, but which may be a sensible option?

You just happen to have a relatively simple partition scheme … but others may have /home and /usr or other partitions … such cases making the use of these different options more readily apparent.

Although that does leave me wondering what happens if you choose different passphrases for Encrypt system and each of the partitions to be encrypted?

If I had a spare system I could test out the various combinations of options to see what happens, but I do not have a spare system, so may be I could investigate the Calamares issues on GitHub to see if the ambiguity has been raised before.