[BrandoElFollito]

An example where such a clone is useful : I run Ubuntu 18.04 and wild like to switch to 20.04.

Since the 18.04 has a history of experiments more or less successful, I want to start from scratch.

I want to be able to rollback in case something goes wrong, but I have only one M2 drive for my system.

So cloning to an external drive, making sure I can boot from it and then delete the existing system gives me peace of mind.

[codethief]

I would counter that by suggesting that you create a second root partition (on which you then install Ubuntu 20.04) and remove the first partition (containing Ubuntu 18.04) when you're done. This is similar to how A/B upgrades work in recent Android versions. (Of course you'd have to have /home on a separate partition. Personally, I've been doing that for years, anyway, because I want to be able to reinstall quickly without overriding /home when a software upgrade happens to mess up my system.)