Any attack with catas get an instant 33% bounty for the 100% resources the buildings destroyed cost related.
what does this mean? a normal cropland cost 62580 from 1 to 10
by example, if 40 catas double shot destroy 2 cropland from 10 to 0 it means you get a bounty of 33% of those resources = 41303 (0.33 x ( 62580 x 2) )
how many of each resource? 11563 14870 11563 3307 (33% of the total cost the owner payed for the building)
now, this is the interesting part
same as inf/cav, catas should have a maximum load, so each catapult suppose maximum carry is 1k
for 40 catas you got 40k capacity, but cause the bounty is 41303 you lose 1303 of the price and return with 40k resources extra from the building demolish (with the specific wave)
so... when we talk about level 18 croplands, or level 20 treasury/tournament square this became crazy for the attacker potential reward above the available resources in warehouse/granary.