All countries require some confirmation you can pay for the stay and will get out. Some countries ask for a return ticket and hotel stay - it indicates that the traveller has some means of paying those amounts. US does not need those before visa issue. In many cases, people cancel the flight ticket after visa issue; and definitely book a more suitable hotel.

Anecdote time: Interpretation of the guidance is upto the visa issuing officer. Normally they want a ticket getting out of the destination country. But in one case the officer wanted me to 'return' back to the country where I was starting the travel from. So I had to show him the ticket for the third leg of the flight: A -> B -> C -> A

To increase your chances of getting the visa.

Sometimes it's even required. I traveled to Nigeria from the US (on a British passport) and needed to turn up to the visa appointment with proof of flights and accommodation.