Ah, ok. It sounded like one or the other (i.e., people who inflate their refund aren't planning well) but personally I find that adding withholding at an amount

Ah, ok. It sounded like one or the other (i.e., people who inflate their refund aren't planning well) but personally I find that adding withholding at an amount that often leads to an inflated refund is a good low-effort way of minimizing risk of underpayment penalties (and it eliminates the need to think about estimated payments) for those good years where substantial gains unexpectedly occur. Of course it's like giving a free loan, which isn't great, but it's miniscule relative to the time I get back by thinking less. And I definitely minimize my liability -- loss harvesting, avoid short term gains, etc. -- so I am squarely in both camps.