You don't 'need' a beauty dish, it's just a tool like any other.
A beauty dish comes into its own when you want a very crisp light above and dead square to the face, that creates shadows that emphasise high cheekbones, that creates a sharpish shadow immediately below the bottom lip and which leaves the neck in shadow.
An umbrella doesn't produce a light that's anywhere near it, but a reflective umbrella can still produce a soft yet crisp light, and a standard reflector fitted with a honeycomb (used very close) can produce a fairly similar effect to a beauty dish.
