Timeshift works in two modes: Rsync mode and BTRFS mode.
In the rsync mode, snapshots are taken using rsync and hard links, and
common files are shared between the snapshots to save disk space.
the BTRFS mode, snapshots are taken using the BTRFS file system. BTRFS
is supported on only systems having an Ubuntu-type subvolume layout.
- BTRFS is a filesystem that needs it own partition to store its backup.
- RSync could save data anywhere, it's more flexible.
I have Rsync option checked in my TimeShift settings, because it is easier to setup than BTRFS— I use TimeShift to restore from little oopsie like theme misconfiguration, wrong package version etc. it's work quite well.
If you required more intermediate case, go for BTRFS then. You're creating a snapshot of your system on the same partition to which you can roll back.