As mentioned before, when a cultivator enters the Core Formation Realm, they need to feed their core part of their own souls. It will leave a severe injury right after the process that can't be healed without a lot of time. But the Soul Healing Pill can heal the soul instantly!
It is different from the Stabilizing Soul Technique. The technique simply represses the injury in the soul temporarily, while the cultivator deals with the Heavenly Tribulation. But the cultivator still needs to take his time to slowly heal it after. If the cultivator gets the soul restored right after the core is fed, their chances of succeeding against the Heavenly Tribulation is increased several times. The Soul Stabilizing Technique is excellent, but it can't be compared with the Soul Healing Pill.