You could model more of the process: the dev's work as well as the model's, and the cost of catching a bug later or deploying it live. Those tasks push me further towards smaller tasks in general. (And they make the Gas Town type stuff seem more baffling.)
- Smaller chunks make review much easier and more effective at finding bugs, as we've known since long before LLMs.
- Greater certainty provides a better development experience. I've heard people talk about how LLM development can be tiring. One way that happens, I think, is the win-or-lose drama of feeding in huge tasks with a substantial chance of failure. I think if you're succeeding 95% of the time instead of 70%, and the 5% are easier to deal with (smaller chunks to debug), it's a better experience.
- Everything is harder about real-world tasks because they aren't clean verifiable-reward benchmarks. Developers have context that models don't, so it's common that a problem traces to an detail not in the spec where the model guessed wrong. For real-world tasks "failures" are also sometimes "that UI is bad" or "that way of coding it is hard to maintain." And it's possible to have problems the dev simply doesn't notice. The benchmarks' fully computer-checkable outcomes are 'easy mode' compared to the real world.
- Fixing agents' mess becomes more work as task sizes increase. (Like the certainty thing, but about cost in hours than the experience.) Again, if the model has spat out 1000 lines and stumped itself debugging a failure, it'll take you some time to figure out: more time than debugging 250-line patch, and the larger patch is more likely to have bugs. And if an issue bug makes it out to peer review, you can add communication and context-switching cost (point out bug, fix, re-review) on top of that.
- Bugs that reach prod are really expensive. More of a problem when a prod bug can lose you customers vs., say, on most hobby things. Ord's post gestures at it: there are "cases where failure is much worse than not having tried at all." That magnifies how important it is the review be good, and how much of a problem bugs that sneak through are, which points towards doing smaller chunks.
How significant each factor is depends on details: how easy the task is to verify, how well-specified it is (and more generally how much it's in the models' wheelhouse, and how much in mine), how bad a bug would be (fun thing? internal tool? user facing? can lose data?).
I think the dynamics above apply across a range of model strengths, but that doesn't mean the changes from say Sonnet 3.7 to Opus 4.5 didn't mean anything; the machine getting better at getting the info it needs and checking itself still helps at shorter task lengths. Harness improvements can help, e.g. they could help keep models of the 'too much context, model got silly' zone (may be less severe than it once was, but I suspect will remain a thing), build better context, and clean up code as well as spitting results out.
Besides taking more of your time up front, involving yourself more also tends to drift towards you making more of the lower-level decisions about how the code will look, which I find double-edged. You have better broad context, and you know what you find maintainable. But the implementer, model or another person, is closer to the code, which helps it make some mid-to-low-level decisions well.
Plan modes and Spec-Kit type things can help with the balance of getting involved but letting the model do its thing. I've liked asking the LLM to ask a lot of questions and surface doubts. A colleague messed with Spec-Kit so it would pick one change on its fine-grained to-do list at a time, which is a neat hack I'd like to try sometime.