Why do I need two blades for my Philips OnionChef?

The regular blade unit is intended for chopping different ingredients (e.g. herbs, raw meat, nuts, Parmesan cheese,…..) finely

The onion chopper blade unit is mainly intended for chopping onions, but it can also be used for chopping other ingredients (e.g. cooked ham and chicken breast, cheese, vegetables, fruit,..) into small pieces