It has two modes, and they use memory a little differently. This is from the manual.
“There are two types of Instancing Modes. Type 1 uses the plugin API’s Copy function and
is generally best for small numbers of complex stamp objects. Type 2 duplicates objects
polygon-by-polygon and vertex-by-vertex. The benefit is that the memory used by textures
and materials isn’t duplicated for each instance. This mode is best for create huge numbers
of simple objects such as grass or fur. This mode is also required in order to use the Bend
Deformation type.”
Placer is a great plugin. I have bought several plugins, Placer and Dante are the only ones I use on a regular basis.
brian