MonoBehaviour.useGUILayout

Description

Disabling this lets you skip the GUI layout phase.

It can only be used if you do not use GUI.Window and GUILayout inside of this OnGUI call.

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour
{
    public void Start()
    {
        //Disabling this lets you skip the GUI layout phase.
        useGUILayout = false;
    }
}