Internally all Forest objects are converted to native instances of V-Ray, so there is not performance loss using meshes instead proxies.
Here is a brief list about pros and cons between meshes / proxies:
- The geometry is loaded in memory while all rendering time (only a copy by tree model). This takes more space in the max scene, although you can fix it using XRefs.
- Any geometric object can be used as source, including parametric and animated objects (Onyx, GrowFX or other Forest object).
- The animation samples are generated on the fly, allowing to create endless animations, but this may be slow depending of the type of object.
- Some Forest features as Tint by Element only can be used with objects.
- The geometry is loaded/unloaded from disk dinamically, only when it is required by the current rendering bucket. This optimizes the use of the memory, but usually is slower.
- The proxies doesn't take space on the scene, but they must be created manually before rendering. Also you must take care to make them visible to all render nodes.
- You can store the animation on the proxy file. It is much more faster to load the samples from disk, than generate them at each frame.
We suggest to use proxies only if the system is low in RAM. But since each scene is different, always is good to test both methods for a specific configuration, specially when creating huge scenes.