Creating Levels of Detail (LODs) for your meshes can be a good way to increase the performance and frame rate of your game without sacrificing visual quality.
In general, the more triangles your meshes have, and the smaller those triangles are on screen, the harder it is for your GPU to render them. Trying to render too many detailed meshes all at the same time can slow down your frame rate. However, you typically don't need every mesh in the scene to be rendered with the same fidelity: when a mesh is far away, you are often able to swap it out for a less-detailed version of the mesh that contains fewer triangles without a noticeable difference in visual quality.
Unreal Engine 4 offers a built-in LOD management system that automatically chooses the most appropriate version of a mesh to show at runtime, based on the amount of screen space the mesh is currently occupying in each frame. This system relies on you setting up these different alternative versions of your meshes in the Editor ahead of time.
The Editor can generate these Levels of Detail for your Static Mesh assets automatically, by progressively simplifying the mesh to thresholds that you specify. For more information about how this system works and how to set it up in the Static Mesh Editor, see Automatic LOD Generation.
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However, even though the Editor can generate these LODs automatically, it may not be feasible for you to open every Static Mesh Asset in your project one-by-one in order to set them all up. You could bulk edit the Assets, but this doesn't help if you want to apply different settings to different Static Mesh Assets based on their characteristics. For example, you might want to apply different reduction settings based on the number of existing triangles in the mesh, or based on an Asset naming convention. It also doesn't help if you want to create your LODs as a sub-step within a larger custom Asset pipeline that you've scripted. For these kinds of cases, you can use Blueprints or Python to script the automatic LOD creation system.