you also need to begin with a really level ceiling, as there is no wiggle room.

most photos have molding, but not all....

Are we really talking "trim" here? Or are we talking soffit? Your designer's comment would make sense applied to a soffit, but not to trim. Taking cabinets all the way to ceiling (actually, to within 1-2" of ceiling, hence eliminating the need for a soffit) is a great idea. However, trying to do this without trimming the top, yet still having it look good is semi-impossible. The reason is that ceilings are not perfectly level, and without any trim this gap would be an uneven dark line that would spoil the appearance, making the installation look messy and amateurish. Well-chosen and well-cut trim can conceal this gap and avoid highlighting ceiling inconsistencies. Any decent cabinet installer can clarify this for you.

Shadow lines are popular in very contemporary spaces. But to have the whole ''no, trim'' thing work involves redoing the ceiling with shimming, strapping, and new level drywall. Nothing looks worse than trying to butt cabinets to a wavy potato chip of a ceiling.

We are indeed talking about trim here. Not soffit.

Thanks for the responses everyone. The feedbacks might have saved us from making a huge mistake. We shouldn't go with no trim.
reasons:
1) The kitchen is not contemporary. It's white shaker cabinets with Rocky Mountain granite top and white subway tiles for backsplash.
2) We love the trim look.
3)Our ceiling is sloped already with 0.5 inches difference from one end to the other.

Then you need at least a 2 piece, and possibly 3 piece crown molding to disguise the slope.

I think trim less cabinets are perfect to save space. The
space will probably be just minimal and you can discuss the remedies with your
designer on what to do with the gaps. Are you planning to have a modernized
kitchen? Or contemporary?

I might answer your question differently for an 8' vs a 9' ceiling.

In a kitchen with an 8' ceiling and when cabinet storage is critical I have compensated by decreasing the space between the countertops and bottom of wall cabinets. This is one way to have crown and not lose storage.

If you do this, measure all countertop appliances to make sure they will fit and make sure the wall cabinets in the cook surface zone will pass code.