optimize, some of your points have been addressed in previous responses.
Because of how our brain processes reflections, how we perceive reflected sound depends on how long those reflections are delayed compared to the direct path from source to ear. If the path of the reflected sound is longer than about 6 meters longer than the direct path from the source to the ear, the reflection will add to the spaciousness of the room. Any reflection that is shorter than that will generally not be distinguished as a separate sound and will result in a spacial smear. Another consideration is that the dB level of sound decreases as the distance increases, and the dB level further decreases every time it bounces off of another surface. It has been my experience that reflections that have a path about 2-4 meters longer than the direct path are especially detrimental to precise localization of instruments and voices if those reflected signals are not at least -20 dB compared to the direct sound.
So the answer is that some reflections off of side walls are beneficial, and some are detrimental. I have left the sidewalls of my room untreated from about 0.5 meters forward from the first reflection point to the front corners. Doing so gives me better sound stage width at the expense of increased slap echo. I've devised a way to deflect the first reflection point away from the ear, which results in superb imaging in my rather narrow (~4.5 meter wide) room. My approach is different than traditional absorption or diffusion. It is more consistent with the approach described by Duke LeJuene above.
That side point will act as a muted bass shy speaker that is delayed as it were placed further away..
Can this side walls reflection points contribute to a wider sound stage?
Or some other benefits that can be a argument to not treat side walls reflections?
Because of how our brain processes reflections, how we perceive reflected sound depends on how long those reflections are delayed compared to the direct path from source to ear. If the path of the reflected sound is longer than about 6 meters longer than the direct path from the source to the ear, the reflection will add to the spaciousness of the room. Any reflection that is shorter than that will generally not be distinguished as a separate sound and will result in a spacial smear. Another consideration is that the dB level of sound decreases as the distance increases, and the dB level further decreases every time it bounces off of another surface. It has been my experience that reflections that have a path about 2-4 meters longer than the direct path are especially detrimental to precise localization of instruments and voices if those reflected signals are not at least -20 dB compared to the direct sound.
So the answer is that some reflections off of side walls are beneficial, and some are detrimental. I have left the sidewalls of my room untreated from about 0.5 meters forward from the first reflection point to the front corners. Doing so gives me better sound stage width at the expense of increased slap echo. I've devised a way to deflect the first reflection point away from the ear, which results in superb imaging in my rather narrow (~4.5 meter wide) room. My approach is different than traditional absorption or diffusion. It is more consistent with the approach described by Duke LeJuene above.
The first sidewall reflection point matters in the design of a recording studio control room. Those I have been involved in used angles which direct the reflections away from the normal listening position.If I read your post right, your room is less than 2 M wide. I don't know how your room is laid out otherwise, but it seems likely to me that your side wall first reflection points have a delay of less than 5 milliseconds compared to the direct signal. Some say that those very short delays don't compromise imaging as much as those having a delay of 5-20 milliseconds. So you may not get much benefit from trying to treat your sidewall first reflections as others.