related: Mesh Instances vs Merged mesh
I don’t have anything to add myself from the above
Both Instancing and Merging the Meshes will reduce the draw calls similarly, so that perf gain you get w/ both
for Instances, there is less data being transferred to the gpu, so for really large diverse scenes you won’t choke the bus
Maybe you get more fps w/ merged meshes cuz it doesn’t do frustum culling (as brought up in the tagged topic) so your cpu is having an easier time
For different kinds of optimizations you can do w/ instances, you can use Thin Instances, SPS, even remove culling for your normal instances
checkout this deep dive about copies
also check out the more general optimization tricks