it's a preference thing - but your designer may have suggested it so you can hang a tea towel on it easier ?! personally I'd use the same handle as the rest of the cabinets ( or if knobs - a pair on it ) as I prefer my appliances to remain as invisible as possible !

Hi Roxanne, that's an interesting decision. Would you happen to have a photo of your current dishwasher, the dishwasher panel, and the cabinets ?
Here's one Miele dishwasher with a built-in handle --

For built in appliances it is common for people to use appliance sized pulls. Decorative hardware manufacturers offer coordinating suites of hardware so that you can get an over sized pull that matches the rest of the hardware in the kitchen. There is no wrong answer but an over sized pull can be easier to use. It has a larger area for your hand to grip and it can be a handy place to hang a dish towel.

You DO want a larger pull... these integrated dishwashers require a strong yank! I would avoid using 2 knobs since you will have to pull on both to open the dishwasher and that means 2 hands to open it.