According to React Final Form documentation, I can pass onChange callback to <FormSpy /> component to execute code when form state changes. However, I also discovered that if I need to run some function every time when the form changes, I can also put this function inside Form's render callback before return statement:

<Form
   onSubmit={onSubmit}
      render={({ handleSubmit }) => {
         myFunctionToRunOnChange(); // Call function here
         return (
            <form onSubmit={handleSubmit}>
               <div>
                  <label>First Name</label>
                  <Field name="firstName" component="input" placeholder="First Name" />
               </div>
               <button type="submit">Submit</button>
            </form>
        );
   }}
/>

Is it good practice? For example, comparing with using FormSpy for onChange...