What is the purpose of the following Script?

Hi, I am following a Lynda course(Advance 2D Platformer). In the first lesson, they are creating a custom made input manager. I attached the code. My questions are, What is the main purpose of using this? Can't we use the simple method (Input.GetAxis())? Explain me please. I just learned some basic stuffs and moved on to this and this is just confusing me. Sorry for my poor English.

InputState.cs

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 
 public class ButtonState{
     public bool value;
     public float holdTime=0;
 }
 
 public class InputStates : MonoBehaviour {
 
     private Dictionary<Buttons, ButtonState> buttonStates = new Dictionary<Buttons,ButtonState>();
 
     public void SetButtonValue(Buttons key, bool value){
 
         if(!buttonStates.ContainsKey(key))
             buttonStates.Add(key,new ButtonState());
 
         var state = buttonStates [key];
 
         if(state.value && !value){
             Debug.Log("Button "+key+ " release "+ state.holdTime);
             state.holdTime = 0;
         }else if(state.value && value){
             state.holdTime += Time.deltaTime;
 
             Debug.Log("Button "+key+ " down "+ state.holdTime);
         }
 
         state.value = value;
     }
 
     public bool GetButtonValue(Buttons key){
         if(buttonStates.ContainsKey(key))
             return buttonStates[key].value;
         else
             return false;
     }

InputManager

     using UnityEngine;
 using System.Collections;
 
 public enum Buttons{
     Right,
     Left,
 }
 
 public enum Conditions{
     GreaterThan,
     LessThan
 }
 
 [System.Serializable]
 public class InputAxisState{
     public string axisName;
     public float offValue;
     public Buttons button;
     public Conditions condition;
 
     public bool value{
 
         get{
             var val = Input.GetAxis(axisName);
 
             switch(condition){
             case Conditions.GreaterThan:
                 return val > offValue;
             case Conditions.LessThan:
                 return val < offValue;
             }
 
             return false;
 
         }
     }
 
 }
 
 
 public class InputManager : MonoBehaviour {
 
     public InputAxisState[] inputs;
     public InputStates inputState;
 
     // Use this for initialization
     void Start () {
 
     }
 
     // Update is called once per frame
     void Update () {
         foreach(var input in inputs){
             inputState.SetButtonValue(input.button, input.value);
         }
     }
 } 

SimpleMovement.cs

 using UnityEngine;
 using System.Collections;
 
 public class SImpleMovement : MonoBehaviour {
 
     public float speed;
     public Buttons[] input;
 
     private Rigidbody2D body2D;
     private InputStates inputState;
 
     // Use this for initialization
     void Start () {
         body2D = GetComponent<Rigidbody2D>();
         inputState = GetComponent<InputStates>();
     }
 
     // Update is called once per frame
     void Update () {
 
         var right = inputState.GetButtonValue(input[0]);
         var left = inputState.GetButtonValue(input[1]);
         var velX = speed;
 
         if(right || left){
             velX *= left ? -1 : 1;
         }else{
             velX = 0;
         }
 
         body2D.velocity = new Vector2(velX, body2D.velocity.y);
 
     }
 }