Net gamma exposure sums the book into one figure: positive means dealers broadly damp moves, negative means they amplify. It is a genuinely useful regime read and it is a summary statistic, with a summary statistic’s weakness.
The same number, two books
Consider a book with one enormous strike near spot and nothing else, and a book with gamma spread evenly across a wide range. Both can total the same net figure.
They will not behave alike. The concentrated book pins hard near that strike and does almost nothing away from it. The distributed book applies mild pressure everywhere and pins nowhere. A trader told only “net gamma is positive” cannot distinguish a market that will sit still from one that will drift freely.
What the profile adds
Where the effect lives. Gamma concentrated at one strike creates gravity there and nowhere else.
Where it stops. The edge of the gamma is where dampening ends, and price crossing out of it enters a different regime without the aggregate necessarily changing sign.
How close the regime change is. Distance to the flip matters as much as which side of it you are on, and the aggregate does not carry that.
Why the crypto book makes this worse
Because it is thinner and more concentrated. On an index book gamma is spread across many strikes and expiries, so the aggregate is a fair summary of a smooth shape. In crypto, and especially below the majors, a few strikes can dominate — sometimes a few strikes created by a single block trade.
When the shape is lumpy the summary is least representative, which is precisely the situation where people reach for a single number.
The rule
Use the aggregate for the regime and the profile for the levels. If only one is available, the profile is the more useful of the two — you can read the regime off the shape, but you cannot recover the shape from the total.