Also more flight restrictions and more discrete spying, ability to lock your drone remotely, and DJIs DroneID broadcasting without your consent.
Because the new firmware implements protections and changes for benefit of the manufacturer, and not for the user.
It will often lock your drone. Disable it remotely. Will not allow you to fly until you comply with the FW upgrade.
If your drone was not locked, this means you haven't updated to the locking functionality yet.
Every update has a chance of failing and bricking your drone for good. The manufacturer might repair the drone, but often you will still have to pay something. And for Phantoms, they will actually tell there's no longer support and that's it.