Creating a single mesh out of the multiple modules.
Having modular examples in your scenes will not affect performance in any noticeable manner unless you have hundreds of spaceships in your scene. But if you are on a very tight budget and can't use the modular examples and cannot find anything suitable in the pre-prepared baked examples made from a single mesh (i.e. examples). You can always bake (i.e. as in attach all objects into one) your newly created meshes using external tools. For instance, by building your examples in Blender, joining them and then exporting back to Unity.
For practical example on how to improve performance by assembling a Spaceship in Blender and exporting as a single mesh you can check the USC Overview Video here:
