More and more people are not laying a layer on their kitchen cabinets

The kitchen cabinets are nothing more than hanging cabinets and floor cabinets. You can freely create articles on the color, layout, and shape of the cabinets, just like this:
But recently I have been attracted by my friend's new kitchen. Not only have I split the kitchen cabinets into two and made them double decker, but the wall cabinets have also shrunk by about 8 centimeters. Why? Isn't this undoubtedly reducing the storage space of the cabinet?
Actually, it's not the case, "my friend smiled and said to me," More and more people are not building one layer of kitchen cabinets anymore. They are adding an extra layer to reduce the wall size by 8 centimeters! A single-layer embedded wall cabinet room is not very useful for storage, but this "double-layer embedded wall cabinet" has twice the storage function compared to a regular kitchen wall cabinet! Moreover, this 8 cm reduction was intentional by the designer.