It runs off a USB stick and presents a pristine system each time you boot. Modifications to the filesystem go on a ramdisk "overlay", which disappears as soon as you power it off.
It does support "encrypted persistent storage", but there is quite fine-grained control over what things are allowed to go in it. In particular, nothing to do with the web browser persists across a reboot unless you go quite far out of your way to make it persist. And each time you boot, you can opt not to unlock the persistent storage if the work you want to do is either liable to get you infected with malware, or just doesn't need any of your persistent data.
Additionally, all of the networking is done over Tor, and the firewall blocks non-Tor traffic, so you can't even miss out Tor by accident. (But if you don't want to use Tor, it's probably not for you, although having used Tor in the past, I was pleasantly surprised how much faster it is now than it was then).
EDIT: And for those who don't know, OP is developer of https://www.qubes-os.org/ which I tried out for a while, and really like the premise of, but found just slightly too inconvenient to use, and I currently prefer Tails.
Qubes has multiple container VMs. All applications run inside a VM, but the I/O is transparently multiplexed into one desktop environment. The window decorations tell you which VM each application is running in. You can copy and paste, and share files, between different VMs, but only where you explicitly want to. You can create VMs to separate data for different purposes (e.g. one just for email, one just for web browsing, and different ones for working on different projects). The VMs can even run different OS's, and there are VMs included by default that route all of their internet over Tor. It is great.