If you want to go up in class and the cc method measures within the upper and lower class limits, there you are.
If you want to go down in class and wished to declare just the allowed overbore in bikes only, the direct measure is for you.
Both with the same assembly.
Car guys will just have to eat it with no overbore allowed.
If the tech guy was getting smart and wanted to save time they might select the jug to measure instead of the entrant.
Cheaters are not as common as dummies and not as common as smart people either.