You'd want it for integrating PWM control, presumably. I'm not a fan of Corsair's software (or anyone's really, for RGB), but it's more than just lighting - you'd want to have the fans controlled through iCue regardless, and I'm not sure if there's a way to do that reliably or at all.
Basically, unless iCue can control motherboard fan headers, something that's certainly possible but also variable board to board, or there's a way to add PWM control channels with the appropriate 4-pin connectors for PWM fans to an iCue-controlled 'system', then these fans are going to be controlled separately. Not the end of the world but I'm surprised that Corsair didn't have a single solution put forth for integrating these fans with the rest of their ecosystem.
I'll say that the bigger problem would be in trying to use these for custom loops, which is also something Corsair is knee-deep into. You'd typically want to tie fan speed to water temperature which without an integration option means using a separate temperature sensor for water that can be monitored by the motherboard (usually more expensive boards at that), and then controlling the fans through the board.
I really would have expected Corsair to have had an integration option linked on the fan page. They don't even have pictures for the fan cables themselves at the moment.