Reducing Performance Costs For Levels

Hoping you guys might share some of your experiences with reducing performance costs for your levels. The main thing I’ve been using is the GPU Visualizer (I access it with LCTRL + LSHIFT and the comma (,) key) and try to see what I can comprehend from there. I notice lights do take up a considerable amount of cost, so I only set the most important to stationary or moveable.

Also trying to cut performance costs by setting certain static meshes to cast no shadow.
Level streaming has helped a lot to reduce load times if you become experienced with that workflow. Also read about methods like merging actors and using instanced static meshes. Would love to hear your thoughts and methods. Thanks.