A heavy pan produces more even results than a thin one of the same diameter and material. The reason is that a pan is a heat reservoir before it is a cooking surface.
Mass stores heat that food removes
Cold food dropped into a hot pan pulls energy out of the surface immediately, and the temperature at the contact point falls sharply in the first seconds.
A thick base holds a large reserve of stored energy and gives it up slowly, so the surface temperature dips slightly and recovers, keeping the searing reaction going.
A thin base holds almost nothing in reserve, so the same food drops the surface below searing temperature and the food begins to steam in its own liquid instead of browning.
Conductivity spreads heat sideways
Burners heat a ring or a spot rather than the whole base, so the pan has to distribute that energy across its surface before it reaches the food evenly.
Aluminium and copper move heat sideways quickly, which is why clad pans place a layer of one of them between steel surfaces that would otherwise conduct poorly.
Cast iron conducts relatively slowly but holds a great deal, so it evens out over time rather than instantly, which is why it rewards preheating and punishes impatience.
Hot spots come from geometry as much as material
A base that has warped, even slightly, contacts the hob unevenly and creates a region that runs hotter than the rest regardless of what the pan is made of.
Thin pans warp more readily because rapid heating expands the base faster than the rim, and repeated cycles leave permanent distortion.
Induction hobs make this more visible, since they heat the base directly and any gap in contact shows up as an untouched patch in whatever is cooking.
Weight has real costs
Heavy pans are slow to respond, so lowering the flame does not lower the cooking temperature quickly, and a sauce approaching a boil cannot be arrested by turning the dial.
They are also hard to lift, tilt and pour, which matters for tasks involving frequent movement or for anyone cooking with limited wrist strength.
Delicate work often goes better in a lighter pan precisely because the cook retains control over the temperature from moment to moment.
Choosing by task rather than by set
Searing, shallow frying and anything where browning is the point benefit most from mass, since that is where temperature recovery decides the outcome.
Sauces, eggs and quick sautés benefit from responsiveness, and a light pan with a conductive base serves them better than a heavier one.
Matched sets rarely reflect this, which is why two or three well-chosen pans usually outperform a full set bought together.