The most common situation I saw was where the entries from the dictionary were being iterated over and used to perform edits on a structure whose edits were nearly commutative.
For example, suppose you have a dictionary containing PriorityItem values. PriorityItems are sorted by priority, while the value only matters for equality (affects __eq__ but not __lt__). If you have a dictionary whose values are PriorityItems and you say `sorted(dictionary.values())` the order of the output could vary w.r.t. equal priority items. So if you wrote a test asserting a process hiding a dictionary had a stable ordering of the items, it might consistently pass by accident on your machine and then fail elsewhere.
For example, suppose you have a dictionary containing PriorityItem values. PriorityItems are sorted by priority, while the value only matters for equality (affects __eq__ but not __lt__). If you have a dictionary whose values are PriorityItems and you say `sorted(dictionary.values())` the order of the output could vary w.r.t. equal priority items. So if you wrote a test asserting a process hiding a dictionary had a stable ordering of the items, it might consistently pass by accident on your machine and then fail elsewhere.