Futon beds
The futon bed originated in Japan where it was not a bed at all,but rather a lightweight mattress and quilt that could be folded up and stored during the day. Its origins laid in the fact that space was limited and therefore anything used for sleeping had to be removed for daytime use. This was a necessity.
Strictly speaking a "real" futon should be laid out on a floor and it will not have a frame or alternative use. However, the definition of a futon has become clouded and, in the western world, both frame and transposable futons are now the norm.
The result of this is that there are many different futons available and this means that you can find one for almost every situation, location and anticipated use.
Modern futons
Modern futons are more sophisticated and, rather than folding away for storage, convert into an alternative use daytime item of furniture. This will most commonly see a futon bed become a chair, sofa or couch when it is no being used as a bed.
This means that the modern futon is a duel purpose piece of furniture and this makes it equally at home in a living room or utility space as it is in the bedroom.
Most futons are bought with the intention of occasional bed use for short term guests and this means that they can be very stylish and made of different material and fabrics. This has become so much the case that there is now a very fine line between what is referred to as a futon and what is referred to as a sofa bed.
Futon options
The typical retail futon bed is based on a changeable or configurable frame that folds or disassembles. This enables it to be quickly changed from a put-up bed to any of the following.
A single chair
A two or three person sofa
A couch
A day bed
The simplicity or complexity off a futon is also very variable. Some futons are cheap and purely functional whilst others have the appearance of a regular chair or sofa. Most people, in determining what kind of futon to buy, will make their choice based up on what is expected to be the primary use of the futon.
If the main objective of the futon is for sleeping, then it is a true futon. However if the main use of the futon will be as an item of living room furniture then it is really a sofa bed.