What are the benefits of having a twin bed over a single bed for a couple?

In setting the stage for your answer allow an explaination that covers a few things first. Most mattress manufacturers have been in business for well over 100 years and they are one of the few industries that are still manufactured in the USA. Their main goal in the world of beds is to confuse the consumer whereas no two retail stores, in so far as competition, have the same bed. That way the consumer finds it impossible to compare apples to apples and the retail store has more flexibility in pricing their beds and making a higher profit margin.

The confusion does not stop . . . A twin bed is the same as a single bed and you would think that a double would be the same thing as a twin but it is not, it is however the same thing as a full. Whats a full you ask, that could mean anything. Lets review.

A Single and twin are the same, both sleep one person and both are the same size.
A double is the same as a full, both sleep one to two people, both are the same size.
A queen is a queen and nothing else in between. The queen bed sports well enough room for two people and is the most popular of all sizes.
A king size bed is large enough for a family of 7. Just joshing. A king is the royal romp about however, made for lovers and fighters. If you get in an arguement with your significant other you have enough real estate on a king to build a wall, create a moat or pitch your own tent. Note to lovers; you can launch a hot air balloon ride, fly a kite and eat oreo cookies or play tennis.