What are the disadvantages of ISAM?

Could you elaborate on some of the drawbacks associated with ISAM, or Indexed Sequential Access Method? One major disadvantage I've heard is that ISAM doesn't inherently support concurrent access, meaning multiple users can't access and modify the data at the same time without some form of locking mechanism. This can lead to performance issues and potential data integrity problems if not managed properly. Additionally, ISAM's data structure is inherently sequential, which can limit its flexibility and scalability compared to more modern database systems. Can you provide any further insights or examples of how these limitations might impact real-world applications or use cases?