If one is already suffering from an ailment/ weakness of the back, back arches might sometimes not be advisable.  But for everyone else, it is highly recommended to make a regular practice of back arches a part of ones Asana practice – whether simple or complex/ advanced.  A regular practice of arching back helps in maintaining the elasticity and mobility of the spine, improves posture, improves the nervous system, is therapeutic for various physiological and psychological conditions, and brings about a sense of exhileration and upliftment.

Especially in the Iyengar system of practice, there is an immense scope for exploration of back arches: preparatory positions give a flavour and many of the benefits of back arches even to those for whom these positions might not be advisable, the final Asanas have been dissected so that parts can be practiced in isolation. this brings focus to specific areas and actions.  Props make possible those positions that might otherwise be inaccessible, and they also make possible longer stays in back arches.

Note:
Back arches can be exhilerating; they can also be exhausting. Approach unsupported back arches with caution when feeling weak, recovering from illness, on hot days.
People with back injuries/ weakness are advised caution.
people with cervical (neck) and shoulder weakness are advised to be cautious when taking the head back
weaknessWomen during menstruation are advised not to do strong backward extensions.