By setting one of the mid banks sharp, a dissonant pulsing or warbling sound is created. It sounds more like an organ. Typical wet for a Cajun box is 15 cents, also 10 cents is popular or half-wet 7.5 cents for milder effect. Some 3-rows go up 20 cents.
Zydeco players seem to favor wet tuning. Also I have found more wet tuned Cajun accordions in the western Golden Triangle area, whereas most prairie and bayou Cajuns seem to prefer dry.
If you have a wet-tuned box, you can choke (partially close) or close the off-tuned bank for drier/dry sound. If you choke a dry-tuned box, the bank goes flat, so you don't get the exact same effect as the sharp method.