I use GoLand for Go development and WebStorm for Vue and Typescript. This is basic development where I mostly use the hinting (suggestions) for classes, types, etc.
GoLand supports both Go and Vue/TS. If I only use it (and not separately GoLand and WebStorm), what am I missing from the most important features? (the ones wildly used)
All features from WebStorm you can find in GoLand. You just need to install some plugins that don't come bundled with it (NodeJS, for example) through Preferences/Settings | Plugins, as GoLand includes only basic stuff (JavaScript, TypeScript, CSS/HTML editing support, JavaScript debugger, etc.) out of the box.
According to: https://www.jetbrains.com/help/go/faq-about-goland.html#in-addition-to-go-which-web-technologies-does-goland-support
In addition to tools for core Go development, GoLand supports JavaScript, TypeScript, Node.js, SQL, Databases, Docker, Kubernetes, Terraform, and other technologies.