A futon is an essential piece of furniture because it is so dynamic and flexible. It is good to lounge on and to just kick back. Then you can have a friend sleep over with minimal adjustment of other house furniture. (Hint: Try putting a thick velvet blanket on the futon as an under blanket...absolute heaven)

On the contrary, futons are somewhat hazardous to your health. They do not support good posture whatsoever! Any way that you try to sit in them, you either lounge (with your back as crooked as a question mark) OR sit completely upright and be uncomfortable as hell. Take you pick...spinal damage or unpleasantness.

Simple solution: When your futon is in the upright position, try putting a pillow behind the small of your back. Thus, straightening your back and preventing discomfort.