Hash Maps (or Hash Tables) are arguably the most widely used data structure due to their O(1) average time complexity for lookups, insertions, and deletions.

They determine how efficiently data is accessed and modified. The wrong choice can lead to bottlenecks, slow response times, and high server costs.

B-Trees are optimized for systems that read and write large blocks of data, like disks, minimizing the number of disk accesses required.