There are a few ways to get a Mesh displayed in a scene. The primary method is to create an Actor with a mesh, which gives you full functionality to manipulate your mesh. Geoms are the opposite end of the scale. They let you statically insert your Mesh into the scene in a very performant way, but they cannot be moved or manipulated.
However, sometimes you need some middle-ground, and that's where MeshInstancer comes in. A MeshInstancer is a stage node that itself can be moved and manipulated, but allows you to instantiate a mesh multiple times in a way that's fast, and uses much less memory than individual Actors. There are drawbacks though:
MeshInstances can't be moved after instantiation, although they can be removed, or have their visibility toggled.MeshInstances aren't part of the Stage hierarchy.MeshInstances can't have behaviours (although the parent MeshInstancer can).MeshInstancer doesn't currently support levels of detail like Actors do.MeshInstances currently don't support mesh animations.MeshInstances don't currently support material slots.MeshInstancers are great for things like foliage, trees, or rocks - where you want to instantiate the same mesh many times.