Some stuff I can think of: - Hashing can be slower than comparison (or vice-versa), depending on the input. (e.g., imagine if your keys are multi-gigabyte file

Some stuff I can think of: - Hashing can be slower than comparison (or vice-versa), depending on the input. (e.g., imagine if your keys are multi-gigabyte files - hashing them would require reading all of their contents, whereas comparing might only need to read the first few bytes.) - Ordered maps guarantee good worst-case performance. Unordered maps only guarantee average case. Usually you don't need to care, but with adversarial input you might. - Ordered maps can guarantee low latency (well, to the extent your allocator can). Unordered maps can't - they suddenly block your program until the whole table is rehashed. Again, usually you don't need to care, but in some situations you might. - Ordered maps have stable iterators; unordered maps "only" have stable pointers. - Ordered maps have a guaranteed iteration order that depends solely on their contents; unordered maps don't. - Any time the ordering itself is useful (see sibling comment)