I make the choice. I don't really listen to specifics like that from customers. I'm a SaaS, not a consultancy. Instead, I try to fully understand the customer's problem and then provide a solution to it a way that will work for everybody. If it doesn't work for everybody, or is a niche feature, then I probably won't introduce the feature unless I can come up with a way to make it valuable to other customers. Often, the customer doesn't understand the best way to implement something to make it valuable/usable to other customers, or the costs involved i.r.t. to maintenance, but I do.

With an API product, you also have to be picky about new features because once something is introduced, it can't be taken back (assuming you want to maintain backwards compatibility).