Resting steps look like waiting and are the first thing a hurried cook removes. What happens during them cannot be achieved by any amount of additional mixing.
Hydration is slower than mixing
Flour absorbs water gradually, and mixing distributes the liquid long before individual starch granules and protein have taken it up fully.
A dough that feels correct straight after mixing will feel stiffer twenty minutes later, because water has moved from the surface into the particles.
Judging consistency before hydration is complete is therefore misleading, and it is the usual reason a cook adds liquid that later turns out to have been unnecessary.
Gluten relaxes only with time
Kneading aligns and links gluten proteins into an elastic network, and immediately afterwards that network resists being stretched further.
During rest the bonds rearrange into lower-tension positions, so the dough becomes extensible and stops springing back when rolled.
This is why a rested flatbread dough rolls thin and stays thin, while an unrested one contracts on the board and thickens again as it is worked.
Enzymes do quiet work in the background
Flour carries enzymes that break starch into simpler sugars and gently loosen protein bonds, and both processes need time rather than agitation.
The sugars released feed fermentation where yeast is present and contribute to browning where it is not, which is why long-rested doughs colour more deeply.
The protein loosening softens the crumb, so an extended rest changes flavour and texture together rather than only making the dough easier to handle.
Batters behave the same way
A rested batter thickens as its starch hydrates, and the bubbles introduced during whisking partly settle out, giving a more even result.
Pancakes and similar preparations made from rested batter are more tender, because the gluten formed during mixing has relaxed before cooking.
Fermented batters need much longer, since the microbial activity producing their lift and sourness works over hours rather than minutes.
Temperature sets the pace
Every one of these processes runs faster when warm and slower when cold, so a rest in the refrigerator is not the same length of rest at room temperature.
Cold resting is chosen where the fat must stay solid or where slow flavour development is wanted, and warm resting where speed and extensibility are the objective.
Reading a rest as a fixed duration therefore misses the point, since the instruction is really about reaching a state that the cook can check directly.