Dynamic View Distance is a Minecraft mod that makes the view distance dynamic to save resources. The current version is intended to be used only on the client.
If FPS fall below the minimum FPS threshold (on average for 5 seconds) the render distance is decreased and vice versa for maximum FPS.
I really recommend running this mod together with ModMenu and Cloth Config. Cloth Config is required for configuring the minimum and maximum FPS. When not installed the minimum FPS will default to 30 and maximum FPS to 60.