If you're dining at a trendy spot in NYC or SF or LA, then you won't be taking leftovers home simply because portion sizes are small, or you're headed to a bar afterwards, etc. It's a different lifestyle.
But if you go out for dinner in most of the country where portions are supposed to be massive, it's pretty normal that after a round of appetizers, you won't be able to finish more than half your entrée. After eating, the server will ask if you want to "take it home" (sometimes using the phrase "doggie bag") and the answer is almost always "of course, it'll be great for lunch tomorrow", and they wrap it up for you. You're just driving straight home anyways.
If it's a business dinner or a fancy first date then maybe you wouldn't... but also maybe you still would. Leaving half of a delicious steak uneaten is pretty wasteful and can be kind of a bad look.
Feel free to browse the Cheesecake Factory calorie contents if you don't believe:
https://www.thecheesecakefactory.com/sites/default/files/202...
Their chicken katsu entrée, for example, is 2,520 calories. A regular teriyaki chicken plate is 1,550 calories. Of course you're taking it home.