can instancing be used for any mesh, eg say 3 buildings that are in a scene , or should instancing only be used for certain things and over a sertain number . if so can any one tell me please

Hi,
If you know before hand that you'll be drawing certain meshes many times per frame, it is good to create a system which allows meshes to be drawn with instancing. Maybe your 3 buildings become 4 some day or 100 perhaps. I haven't noticed any performance hit coming from using geometry instancing.

Nowadays it is even possible quite easily to have different textures for different mesh instances.

Cheers!