Is it really useful ?
Building a scene with TroisJS is really handy, especially with VueJS and ViteJS HMR.
Using template tags, or custom components, make your code easier to re-use.
And you can easily handle events on meshes, use a physics engine, or add postprocessing effects...
Is there any limitations ?
No, you have access to ThreeJS renderer, scene...
What about performances ?
TroisJS is just a wrapper, it is not slower than ThreeJS (except if you use reactivity too much).
How to dispose ThreeJS objects
You don't have to (except if you have created the objects yourself), TroisJS will automatically dispose geometries, materials, textures, renderer, effect passes...
Why it is important : https://threejs.org/docs/#manual/en/introduction/How-to-dispose-of-objects