Forest Pro Pier (provided by itoo software) scene render by Erwan Loison.
Arion for 3ds Max interprets native 3ds Max instances as Arion instances, so everything that is considered an instance in MAX is rendered as an instance in Arion as well. So, basically, there is no need to do anything special to benefit from instancing in Arion for 3ds Max.
The easiest way to create an instance from an existing object in 3ds Max is to select the source object and translate it while holding the Shift key down. The Clone Options dialog will show up, prompting the user to specify whether the newly created clone should be a Copy, an Instance, or a Reference. If Instance is selected, 3ds Max will treat that new object as an instance, and in render time Arion will replace that object by a singleton point cloud bound to the source object.
As explained in this page, instancing is particularly convenient (even critical) when heavy objects such as trees or plants must be used multiple times in a scene. Memory-wise, the cost of creating a new instance is virtually zero, so basically it is possible to add as many instances as necessary. Note, however, that instances may use up viewport resources in 3ds Max, since they are displayed as a replica of the source object.
Affine transformations applied to an instance (such as translations, rotations, scalings, ...) are also interpreted by Arion for 3ds Max, so it is possible to create multiple instances of a tree, re-position them, re-orient them, and scale them randomly on a field.
This page explains how Arion for 3ds Max makes use of instancing to render particle systems or do object scattering.