A bonus is that you can build out server features a LOT faster when you only have a single app to worry about: you can couple your client and server implementations, and know by just testing on your one client that you haven’t broken it with a server change.

And when you do break things, it’s relatively easy (especially on iPhone where most users upgrade apps quickly) to fix the client, wait for the next release, then remove the unwanted server feature.

Once you have two or more client implementations, you have to keep track of a lot more things, your QA checklist grows, and you therefore need to move more carefully for server upgrades.