With a growing focus on sustainable energy, some hydrogen projects worldwide, including Australia, are currently adopting off-grid structures that comprise variable wind and solar resources, electrolysis plants, and grid-supporting technologies like battery storage systems and synchronous condensers. To reduce capital costs, there is ongoing debate on leveraging electrolyzer flexibility to enhance microgrid stability and minimize renewable energy curtailment. In this context, flexibility in electrolysis plant operation involves the ability to adjust both active and reactive power to support microgrid frequency and voltage stability. Furthermore, flexibility also encompasses the capacity to modify the active power consumption of electrolysis plants, helping to minimize the curtailment of renewable energy generation within the microgrid. This allows electrolysis plants to play a significant role in maintaining overall microgrid stability and maximizing the utilization of renewable energy resources, also reducing the capital cost on additional equipment for microgrid stability enhancement. This paper presents an in-depth study of key factors impacting flexibility provision from H2 electrolysis plants, focusing on electrochemical features such as stack degradation, hydrogen production efficiency, stack ramp-up/ramp-down limits, stack partial loading constraints, and challenges with stack no-load operation. By presenting detailed yet straightforward explanations, we aim to demystify these electrochemical aspects for the power and energy community while offering potential solutions to mitigate their limitations. Additionally, we examine various operational factors that may constrain electrolysis stack frequency control and voltage control support, including downstream hydrogen process/buffer limitations and the nature of hydrogen process within the microgrid. Our comprehensive analysis seeks to provide essential context for electrolyzer flexibility in microgrids and regional hydrogen hubs, ultimately strengthening the business case for hydrogen projects.