Static Mesh Component Instances

Can someone help me understand how to use these?

It’s clear and obvious how to add a static mesh to your blueprint from within the blueprint. Add the component then set the mesh on that component

But what about instances? Does this imply that somewhere I need to have a non-instance?
I don’t need my hands help but I can’t find any documentation about it

I am trouble with my game slowing down due to all the static meshes I am adding, slowing to a crawl. I hope this can help the situation

You add a InstancedStaticMesh Component to your Blueprint set its Mesh and then AddInstance(es) and set their transform all can be done at runtime