this is how i've been using it, and where i've found it really excels over anything else i've tried. get fable to write a plan, and get something cheaper to follow the plan. the code fable writes isn't significantly better than the code opus writes, as long as they're both following the same plan. but a plan written by fable is much better.
The structure of the code is easily readable as I enforce concenventions followed by good libraries. And I can easily plug in new datasets. It's pretty good frankly.
That seems valid in today's world. Right now it's expensive, slow, and accurate. I imagine in the fairly near future it will be cheap, slow, and accurate, and that'll be a great opportunity to let it run on anything time-insensitive.
Re current use-cases: in addition to planning, there's also some tasks which Opus just can't complete but Fable can. Multiple times I've spent hours in combination w/ Opus trying to debug some particularly nasty nondeterministic issue, only to have Fable nail it in 20mins while I walk the dog.
Cybersecurity hardening. The one thing they don't allow the model to do.