FPS drops when I maximize the game tab in Unity Editor

Question

I have a simple unity scene with some primitive objects like cubes and spheres. Most of the objects are static and I made backed GI for lighting, The light is a point light. I also used unity post-processing asset for the depth of field.
FPS in normal game window size is about 500 but when I maximize the Game tab, FPS goes around 30. Why does this happen?

FPS 500

FPS 30

Answer 1

Most likely reason is that you have VSync turned on for your game. VSync (vertical synchronization) will only ever work for a game if it's in exclusive full screen (which is what you're doing by maximizing). You can change this setting by using the QualitySettings option for VSync. Taken directly from the link I've provided. This Example() function should only ever be used when VSync option is wanted as turned off.

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour {
    void Example() {
        QualitySettings.vSyncCount = 0;
    }
}

You can also turn it on or off in the default Quality Settings here (using menu: Edit > Project Settings > Quality).

Both pictures taken from Unity's linked pages, since Unity sometimes likes to change the current manual and deprecate links or images.

There's also one more setting that could affect target framerate. Try setting it to a high value.

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour {
    void Awake() {
        Application.targetFrameRate = 300;
    }
}