Denormalization is not a one-size-fits-all solution and should be used carefully and strategically. When deciding when to use denormalization, there are several factors and guidelines that can help inform the decision. For example, analyze your data and requirements to understand the volume, variety, velocity, and veracity of your data, as well as the frequency, complexity, and purpose of your queries. Additionally, determine the performance goals and trade-offs for speed, accuracy, and consistency. To choose the appropriate level and method of denormalization, consider partial, full, or hybrid denormalization; horizontal, vertical, or aggregate denormalization; and the impact and feasibility of each option on your database design and maintenance. After applying denormalization, test and monitor it to evaluate its effectiveness and efficiency by measuring query performance, data quality, and resource consumption before and after denormalization. Make adjustments or revisions as needed.