One of the recurring themes on the Chowhound website's 'not about food' category is dining etiquette: someone is planning a trip, and asks how to eat according to the customs of that country.
There's always at least one person who asks, 'what's the point of this?' They believe that as long as you can get the food to your mouth and consume it without being too disgusting (even they agree that chewing with your mouth open is wrong), there shouldn't be too many problems, implying that people who care too much about etiquette are shallow.
I grew up in a Chinese household in the US, so I learned the correct way of dining at a Chinese meal, as well as American table manners which include the so-called zig-zag method of cutting food with a knife held in the right hand, putting the knife down and moving the fork to the right hand to pick up the food and put it in the mouth.
After moving to Hong Kong and meeting people from different cultures, I learned the Southeast Asian way that included a fork held in the left hand and a spoon in the right, and using the spoon to eat with. In Korea, I learned (among other things) to keep the rice bowl on the table and use a spoon to eat it. I embraced certain European and English techniques, such as keeping the fork in the left hand, rather than switching it back and forth to the right, American-style. While I love Japanese food, and travel as often as possible to Japan, the table manners there are so complex that, although I try to eat correctly, I hope that I don't make any major faux pas and cause offence to my hosts. And I know in theory how to eat with my hands when I'm in India or the Middle East, but in practice it's much harder to execute gracefully than it looks, so I use utensils.
Although I do my research about dining etiquette before I travel to other countries, I learn mostly by observing others, then copying. I'm sure there are subtleties that I'm unaware of, but so far, nobody I've dined with has pointed them out.
There's a passage in To Kill a Mockingbird that I remember from reading the book many years ago. The child protagonist, Scout, embarrasses one of her classmates because he pours syrup over his food as he's eating lunch at her house. The housekeeper is angry, and says to Scout, 'That boy is your company. And if he wants to eat up that tablecloth, you let him, you hear? And if you can't act fit to eat like folks, you can just set here and eat in the kitchen.'