Sometimes your CEO doesn't completely trust the development team. Sometimes the client wants to make sure the vendor really values them. Sometimes the head of sales decides to take a punt on something that has a small chance of a big impact.
As a development team, the best thing you can do in each of these cases is to build the useless feature. Build it properly, but build it with a minimum of effort, and be ready to retire it and delete the code when it turns out to be useless.
Earn the CEO's trust. Reassure the client. Throw the dice. There are payoffs to work other than value for the end user.