Final answer:
The major disadvantage of the "big bang" approach in HR system integration is the difficulty in isolating the root cause of system failures due to simultaneous system integration.
Step-by-step explanation:
The major disadvantage of the "big bang" approach to HR system integration is that it is difficult to find the root cause of system failures. This approach involves integrating all systems simultaneously, which can lead to increased complexity and challenges in isolating specific issues when something goes wrong.
Unlike incremental implementation, where changes are rolled out in phases, the Big Bang method doesn't allow for easy performance verification in a live environment, because everything changes at once. This can result in operational disruptions and the potential for significant downtime while trying to pinpoint and resolve problems.