Duplicity is very old backup software that uses the "full + incremental" strategy on a file-by-file basis, like tape backup systems. The full backup must be restored first and then all of the incrementals. This becomes impractical over time, so as with tapes, you must periodically repeat the full backup so the incremental chains do not become too long.
Modern backup programs split files into blocks and keep track of data at the block level. You still do an initial full backup followed by incrementals, but block tracking allows you to restore any version of any file without restoring the full first and all following incrementals. The trade-off is in complexity: tracking blocks is more complex than tracking files.
Duplicity is very old backup software that uses the "full + incremental" strategy on a file-by-file basis, like tape backup systems. The full backup must be restored first and then all of the incrementals. This becomes impractical over time, so as with tapes, you must periodically repeat the full backup so the incremental chains do not become too long.
Modern backup programs split files into blocks and keep track of data at the block level. You still do an initial full backup followed by incrementals, but block tracking allows you to restore any version of any file without restoring the full first and all following incrementals. The trade-off is in complexity: tracking blocks is more complex than tracking files.
It has nothing to do with encryption.