Dynamic View Distance (Requires PaperSpigot)
The dynamic view distance improves server performance by dynamically setting view distance in order for the loaded chunks to be close to a static number, while players fluctuate. It does this by calculating the max view distance necessary to maintain the loaded chunks at the configured value.

Not only does this optimize the server when the player count increases, but it also allows your players to have a greater view distance on your server when your player count is low.