What’s the difference between using useRef and directly using watch function in Reactjs?

I’m making a register form with react-hook-form.
I use useRef to compare "password" and "password_confirm".
I know that useRef is used to variable commonly. and the lecture that I heard let me this way.

const {
    register,
    handleSubmit,
    watch,
    formState: { errors },
  } = useForm();
  const onSubmit = (data) => console.log(data);

  const password = useRef();
  password.current = watch("password");

<input
          name="password"
          type="password"
          {...register("password", { required: true, minLength: 6 })}
        />

 <input
          name="password_confirm"
          type="password"
          {...register("password_confirm", {
            required: true,
            validate: (value) => value === password.current,
          })}
        />

this way is using useRef for containing current value of "password" input.
so then, password.current validated with value of "password_confirm" input .
however, I think "Why should I use useRef?"
Because, I can make validation in this way.

const {
    register,
    handleSubmit,
    watch,
    formState: { errors },
  } = useForm();
  const onSubmit = (data) => console.log(data);

<input
          name="password"
          type="password"
          {...register("password", { required: true, minLength: 6 })}
        />

 <input
          name="password_confirm"
          type="password"
          {...register("password_confirm", {
            required: true,
            validate: (value) => value === watch("password"),
          })}
        />

I’m curious that the difference between the way using useRef hook and the another way directly using watch function.