The worrying bit is if you're not keeping a close eye on it, very easy to think you're getting a solid system, but thanks to the internal madness it's used, your entire grid has in effect shifted 10 metres right, and any spatial measurements are far more approximate than it's letting on.
That was the bad old days for me. Nowadays I keep it locked down to specific systems for projections or actual spatial calculations, and that seems to keep it honest.
And the surprise is awesome when it happens! My favourite is all the QA steps you wish you'd had and that it reasons out on the raw data alone:
"oh hey, this one city has no data but it has a high population, oh right, that's because of this obscure lookup had a row chopped off, there you go, sorted."
I get to stand back and applaud it, honestly.
One that has saved me many hours: given a small subset A and a disjoint sample B of a larger set of, say, complicated JSON objects in a consistent but unknown schema, what do the objects in A have in common that isn't true of any objects in B?
Example result from Claude: The field foo contains dates between August 3 and August 7, 2016 in every record in A, and every record in B contains later dates.
Claude even correctly hypothesized that it was dealing with metadata from a document management system, that field foo was the creation date of the document, and that nearby field bar, identically 10 in all records, was the document retention period in years, and thus A represented documents that would have been purged between August 3 and August 7, 2026.
One thing that helped me a ton was making an adapter between my domain specific datasets/systems and QGIS. So I can watch and examine the intermediate steps and leverage that my brain is still pretty darn good at visual pattern matching.
For what it's worth, I use duckdb and its spatial stuff as my adapter. Works for my brain and if you force e.g. SQL files for each step, gets there in the same kind of way. Still some sharp edges, mind, but overall working well. And then Claude comes for my maths and I sob.