I don’t use Tailscale, I use a competing and currently arguably better product (Netmaker).
Imagine you’re a business building XYZ software product. You build a k8s cluster in one region, but now you need your system also to exist simultaneously in another region for failover reasons. Now you need region A to be able to have replicas in region B in real-time amongst many other requirements and those two networks from each region need to be able to understand and talk to each other with minimal setup and headache. Perhaps network A is set up on DigitalOcean and network B is on AWS or GKE for financial or technical reasons. Example: it’s cheaper to have surplus machine needs on AWS/GKE but you don’t want machines running there all the time because it’s expensive.
Enter Wireguard mesh networking. Ever since kernel Wireguard made it into Linux this is where the endgame has been for cloud deployments. It’s a huge improvement over the previous solutions. Netmaker and Tailscale are two offerings of that solution.
Note that I’m not affiliated with Netmaker at all. Just a quite happy customer.