Qubes is basically the Xen hypervisor with a nice VM template system and near-seamless desktop integration for VMs.
In addition to the security provided by putting stuff in separate VMs, it's great for development and other cases where you need to fire up a clean OS install. The integration tools like clipboard and file transfer makes working across multiple VMs practical.
There are several cons and caveats, though:
No GPU acceleration inside VMs (except you may be able to pass a discrete GPU through to a single VM). Forget about 3D design software, games etc. Websites with lots of advanced CSS filter stuff will be slow.
Certain software is slow/buggy, including LibreOffice and Inkscape (probably partly related to the lack of GPU acceleration).
No hibernation (suspend to disk), only suspend to RAM. And suspend to RAM might be buggy or not work at all depending on your hardware.
Many running VMs means high memory requirements. If you use the same computer for lots of different tasks, I'd recommend a minimum of 32 GB, optimally 64 GB of RAM if you want full compartmentalization.
Bugs and poor UX in the Qubes-specific interfaces. A lot of it feels rather hacky. Some of these interfaces could allow for cross-VM exploits if vulnerable, so that is a concern.
Qubes is basically the Xen hypervisor with a nice VM template system and near-seamless desktop integration for VMs.
In addition to the security provided by putting stuff in separate VMs, it's great for development and other cases where you need to fire up a clean OS install. The integration tools like clipboard and file transfer makes working across multiple VMs practical.
There are several cons and caveats, though: