Apart from the reasons stated from @marteng69 the main ‘problem’ is that the default encrypted system calamares sets up leaves you with a single luks encrypted ext4 partition.
I personally ‘need’ a separate /home for multiple reasons. One is described below …
One way of achieving this is setting up /root, /home and maybe a swap ‘partition’ as logical volumes inside a single encrypted partition. You can then make snapshots of these logical volumes and restore these states should you ever want or need to. Of course you probably wouldn’t want/need to reset your /home data (=personal data) every time you reset your base system, hence the separated logical volumes. This sort of install is described in the LVMonLUKS howto.
Another way which is far easier to set up and works with calamares is described in my BTRFSonLUKS tutorial.
Here we get an encrypted system with separate subvolumes for /, /home, /swap and the cached pkg packages. Root and /home can now also be the sources of separate snapshots. Taking and restoring these btrfs snapshots takes about a second followed by a reboot in the case of restoring. (LVM snaphots also only take a second to create but the restore process mostly takes a lot more time and in some cases needs to be done from a different live system). You can even boot into snapshots should you want to.
Both setups provide me with a way to recover from my testing, tinkering or a problematic upgrade in mere seconds!