This is optimizing for the common case, where memory is generally plentiful and dicts grow more than they shrink. Python has so many memory inefficiencies that occasional tombstones in the dict internal structure is unlikely to be a major effect. If you're really concerned, do `d = dict(d)` after aggressive deletion.
I can't say I've noticed any good reasons to rely on it. Didn't reach for `OrderedDict` often back in the day either. I've had more use for actual sorting than for preserving the insertion order.
This morning for example, I tested an object serialized through a JSON API. My test data seems to never match the next run.
After a while, I realized one of the objects was using a set of objects, which in the API was turned into a JSON array, but the order of said array would change depending of the initial Python VM state.
3 days ago, I used itertools.group by to group a bunch of things. But itertools.group by only works on iterable that are sorted by the grouping key.
Now granted, none of those recent example are related to dicts, but dict is not a special case. And it's iterated over regularly.
I don't often care about a specific order, only that I get the same order every time.
Granted, I live and work in TypeScript, where I can't `===` two objects but I could see this deterministic behavior making it easier for a language to compare two objects, especially if equality comparison is dependent on a generated hash.
The other is guaranteed iteration order, if you are reliant on the index-contents relationship of an iterable, but we're talking about Dicts which are keyed, but extending this idea to List, I see this usefulness in some scenarios.
Beyond that, I'm not sure it matters, but I also realize I could simply not have enough imagination at the moment to think of other benefits
But maybe it does all just come down to equality comparisons. Just not always within your own code.
For me, it creates more reproducible programs and scripts, even simple ones.
I would expect to use a different data structure if I needed an ordered set.
