Ninety grams is three quarters of a cup of all-purpose flour, and almost exactly one cup of rolled oats. Those two facts make it a frequent weight in flapjacks, granola and oat-based cookies.
Across the full chart above, this same weight fills 1.07 cups of cocoa powder but only 0.26 cups of honey. Cocoa is the lightest ingredient here and honey the heaviest, and that spread is the whole reason the ingredient has to be named.
Keep the original 90 gram weight whenever the recipe depends on an exact ratio between flour and liquid.