Hydration. Flour doesn't absorb water instantly. Left alone, the starch granules and protein take up water fully, and dough that felt stiff and shaggy at mixing becomes noticeably softer and more cohesive without you touching it.
Passive gluten development. Once hydrated, glutenin and gliadin link up on their own. You get real structure with zero mechanical work — the same organisation kneading produces by force, arrived at by sitting still.
There's enzyme activity too — proteases loosening the protein network slightly, amylases starting to break starch into sugars — which is where the improved extensibility comes from. The net effect is a dough that stretches further before tearing, which makes every later step easier: folds go further, shaping fights back less.
Salt tightens gluten — it's why salted dough feels stronger and less sticky. That's useful later and counterproductive now, when the whole point is to let the network form loosely and extensibly.
Levain starts fermentation. Add it at the beginning and the autolyse hour is really a first hour of bulk, which throws your timing off and drops the dough's pH while it's still trying to organise.
Hold both back, add them together after the rest, and squeeze them through until fully incorporated.
30–60 minutes captures nearly all the benefit for a standard white or lightly-blended dough. Most of the change happens in the first half hour.
Longer isn't better, and past a point it's worse. Protease activity keeps going, and a very long autolyse — three or four hours, especially warm — can slacken the dough so much it never regains structure. If you want to rest longer than about two hours, do it in the fridge.
Whole grain flours are the special case. They carry far more enzyme activity in the bran and germ, so they reach the same point faster and degrade sooner. 20–30 minutes is plenty at high whole-grain percentages, and past an hour you're actively giving up structure.
Autolyse gets treated as mandatory. It isn't, and there are real cases where skipping it is the better call:
High whole grain — the enzyme activity that makes autolyse useful in white flour works against you here. A short rest or none at all.
Low hydration doughs — bagels, stiff levains. There isn't enough free water for the process to do much.
When you're short on time — an hour of clock for a marginal gain in extensibility is a bad trade if it's the difference between baking and not baking. The loaf will be fine.
When you're learning — one fewer step, one fewer thing to blame. Add it once the rest is reliable and you can actually feel the difference it makes.
Notes from the counter
Autolyse has a slightly outsized reputation, and I think it's because it has a French name and a specific rule attached to it. Techniques with names and rules feel like craft. Techniques like "wait longer" feel like laziness, even when they matter more.
It's a real improvement and it costs nothing but time. It is also, on a list of things that determine whether your loaf is good, somewhere near the bottom — well below reading the bulk, below shaping, below having a starter at peak.
Do it when it's convenient. Skip it when it isn't. Don't let it become one of the small rituals that make a hobby feel like homework.