You don't need this for general productivity software, only stuff where QEMU's emulated GPU is too slow or otherwise insufficient (so games, video editing, etc).

The caveats are basically:

1. Setup is a bit annoying

LG can feed input into any VM but requires guest support for capture, so you need to do the setup with a direct monitor.

2. The passed-through card must have a monitor connected.

IIRC, this is an API issue since it just captures what would go to that monitor.

3. Some things are only visible on the real monitor.

They need different capture strategies for the regular desktop, system desktops (such as lock screens), and secure desktops (UAC prompts). Sometimes the transition fails, sometimes there is no strategy implemented for what you're trying to show.

4. Your CPU and motherboard must support IOMMU passthrough.

For Intel this means using Skylake+ and ensuring that it supports VT-d. For AMD this means using Ryzen with an X-series motherboard.

5. You need separate GPUs for the host and guest.

Blame GPU vendors for making VT-g an enterprise-only feature.