Holding dishes is polite in Japan. When eating, the Japanese usually hold their rice bowl, their soup bowl or any other small bowl that can be carried in one hand. Because the Japanese used to sit on a tatami, which is a mat made of straw, and use a low table, lifting a dish to eat became a Japanese custom. Bringing your mouth close to the table was considered rude since it made people think you were behaving like a dog.
Nowadays, as we basically use only a pair of chopsticks to eat, we hold the soup bowl close to our mouths so we can slip the soup directly from it. On the other hand, flat plates, which are used to put the main dish, are not usually lifted from a table since those are too heavy and big to hold single-handedly.
When I was a child, I learned about these table manners from my parents. My mother was strict, and she would point out when I was doing something inappropriate such as eating without holding my bowl. If I had not learned these manners in the past, I could be considered a senseless person.
Therefore, it is important to hold your dishes when you eat Japanese food in Japan. Otherwise, you will be considered impolite in Japanese culture.
I wrote about one of the Japanese cultures.