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619 recipes
Chill it when the recipe says to
A recipe is a system: its flour, sugar and butter were balanced alongside its resting time, so pulling the rest out changes a formula that was built with it in.
That is a different question from whether chilling matters in the abstract, and it is the one that decides tonight's batch. Follow the rest the recipe asks for. Where it asks for none, you are not skipping a step: you are baking a formula that never had one.
How sure we are: sorted into no rest, a short one and a long one, the three groups land close together on every outcome we measured. An effect smaller than the variation between these recipes would be invisible to us, so read this as “smaller than the advice implies” rather than “zero”.
Not the lever
619 recipes
Reach for brown sugar, not the fridge, for chew
Resting time varies enormously across these recipes and the chewy ones sit right across the whole range of it.
This is the claim cooks make most often in our reviews, so it is worth being precise: if chilling were the reliable chewiness lever it gets described as, a corpus this size would show it, and it does not. Brown sugar is the lever that does, because it holds water in the finished cookie. That page is one click away and it is where the effort pays.
A nudge, not a fix
619 recipes
Weigh the flour before you blame the fridge
Recipes that rest longer do come out thicker than average, and the gap is much smaller than the advice around it suggests.
This is the middle ground neither side of the argument occupies. The pages calling chilling crucial are right that the direction exists. The pages calling it optional are right that it will not rescue a formula. If yours are spreading badly, weigh the flour and look at how the butter was handled first: both move a cookie further than an extra night in the fridge.