I've probably said this before, but...

This was one of the things that sold me on Macs. You can easily create a clone of the system drive to any drive, internal or external, and then boot from the clone without unplugging anything. Once you're booted from the clone you wouldn't know* you weren't running from the original drive.

I believe Windows has improved in this area a bit now though ?

* there can be some oddities with DropBox, but that is about it