Forward bends are calming. In yoga classes I always notice their soothing nature as they allow your spine to roll towards a fetal position. Long term many people take on this rolled forward position and form a slouch, primarily in their upper back that I spend time trying to help clients with. Ideally your spine moves within a full range of motion and your soft tissues support good posture throughout your day.
Backbends are the healers of the spine for many reasons but I’d never trade them in for simple forward bends. This seated forward bend you do in Thai massage is done at the end of a session when your client is seated and you’re feeling open, free, unencumbered.
Creating length on the spine is good for the long term health of the vertebrae and posture. Long term it takes pressure off of the discs, prevents herniation, bulges and the like. In yoga you’re working in standing forward bends in turning the whole spine upside down and tractioning it. Usually this is stopped by intolerably tight hamstrings and one should be conscious to stretch the hamstrings and take pressure off of the low back. This is done by gently bending the knees and allowing the torso to rest on the thighs.